Almost all motorcycle have manual transmissions, so you have to change gears to match the engine speed to the road speed. Lower gears (1-2-3) are for lower speeds, and higher gears (4-5-6) are for higher speeds, just like a car.
On most motorcycles you want the engine running between about 3,000 rpm and 6,000 rpm. Below 3,000 rpm the engine is lugging, and does not run smoothly. If you give the engine a lot of gas at low rpms, it will lurch and sputter and generally let you know that it's not at all happy with you. Above 6,000 rpm the engine is starting to make a lot of power, and your speed will increase very quickly. If you try to cruise at such high engine speeds, you'll find the motorcycle is extremely responsive to the throttle and difficult to control smoothly.
To shift, roll off the throttle as you pull in the clutch lever, shift the transmission lever firmly, and then let out the clutch smoothly as you ease back on the throttle.
You can shift to a lower gear, let out the clutch and leave the throttle closed, and the engine will slow the bike down. This is called engine braking. This is perfectly ok as long as the engine speed stays below the red line.
Unfortunately, from time to time you're going to have to stop your motorcycle. Your motorcycle has brakes to let you do this. There are two brakes, one on the front wheel, and one on the back wheel. On most motorcycles, the lever on the right handlebar works the front brake, and the pedal on your right foot works the rear brake.
The front brake on a motorcycle in typical situations has about double the effectiveness of the rear brake. Some beginners are told that the front brake is dangerous and they should not use it. While it's true that you can get yourself into trouble with the front brake, you simply have to learn to use it. If you don't, you will be unable to stop your motorcycle from typical traffic speeds in safe distances - the rear brake working alone is not very effective on a motorcycle. You're simply going to have to practice using your motorcycle's brakes - both of them. You should always use both brakes to slow or stop your motorcycle. Even though one brake alone may be enough in some situations, your motorcycle is more stable when using both brakes, and you should develop the habit of always using both.
Squeeze the front brake smoothly and progressively. It takes a second for the weight to transfer forwards. If you grab the brake lever abruptly, the front wheel can lock up resulting in a front-tire skid. You will lose balance and steering control. If you lock up the front tire, immediately release the front brake to allow the wheel to resume rolling, and then reapply the brake properly. If you're a particularly skilled rider, you can do a front wheel stand, a "brakee." Don't worry, there's no chance you will do this accidentally, it takes a lot of practice.
If you use too much rear brake you can skid the rear wheel. The biggest danger in a rear-tire skid is releasing the rear brake when the rear wheel is out of alignment with the front wheel. If the rear wheel stops skidding and resumes rolling when it is out of line with the direction of travel, the motorcycle will immediately straighten out. This can cause a particularly dangerous crash called a high-side, where you are slingshotted over the bike. Once the rear wheel starts skidding, it's usually best to just keep it locked up. If you learn to ride in the dirt, as I recommend, you will naturally learn this and it will seem like no big deal at all.
Some motorcycles have linked brakes - this means when you pull on the front brake lever, the rear brake is also activated, and when you step on the rear brake pedal, the front brakes are also activated. Personally, I hate linked brakes. I very much prefer the added control of independent brakes. However, some riders on heavier touring machines are perhaps safer with linked brakes.
Some motorcycles have ABS - anti-lock braking systems. These are good things. In tests of the most modern systems, only a very few professional motorcycle racers can out-stop ABS brakes, and that only on dry pavement in controlled conditions, and then only by a couple of feet. If you're in an accident avoidance situation where you don't have all your attention on the brakes, or if you're in a low-traction situation like sand, gravel, or water, ABS out-brakes even professional racers by 100 feet or more from 60mph. Although a lot of old-timers dislike ABS on general principles - computer guided motorcycles somehow seem sacrilege - in fact ABS is a good thing. If you have a chance to get this option on your bike, I recommend you get it.
From time to time you will see obstacles ahead of you on the road. If you're confident you're the only vehicle on the road, slow down and ride around it at a safe speed. On a highway you may not have this luxury. I have seen pretty much everything you can imagine on a highway, including mattresses, tires, furniture, dogs, and strange indescribable thingies. Of course in our south western states they have signs on the highways warning you of illegal aliens crossing the freeway. Really, I'm not clever enough to make this stuff up.
When you see an obstacle that you can't avoid, it's best to stand up on your foot pegs if you can, get your weight as far rearward as you can, and hit the obstacle straight on.
Railroad tracks often cross country roads at an angle. It's best to cross railroad tracks at 90°. This means on country roads you should slow down and drive across the road at an angle so that you cross the railroad tracks straight on.
Some older highways have rain grooves cut into the concrete. These grooves make some motorcycle tires wander side to side a small amount, which can be a very uneasy feeling for a beginner. The motorcycle won't actually fall over - if you stay calm and keep your arms loose, everything will be fine.
Some older bridges have open metal mesh for a roadway. Not only does this make the motorcycle wander, but when you look down you can see right through it. They won't actually make your motorcycle tip over, but overall it's simply a horrible experience. There's very little traction available, so you almost don't have brakes. If you do fall down, the bridge surface is a lot like a cheese grater. Truth be told, I hate these bridges.
When the temperature gets below freezing, there can be a thin sheet of water on the road that freezes. This is called "black ice." It's invisible to a driver. When you hit this stuff, you'll know - I hit some once in Yosemite park at about 10,000 feet elevation. I realized immediately that pulling on the handlebars had no effect - my motorcycle was sliding down the roadway. This went on for about 100 yards before the ice cleared. If you hit the brakes, the wheel stops but your motorcycle does not. This is very bad, as when you're on black ice the gyroscopic effect of the wheels is all that's keeping you up. Fortunately, my motorcycle happened to be lined up correctly and I "slid" the 100 yards without any external incident. Internally, this is an experience called "pucker power," a state where even if your hands and feet were to come off the motorcycle, still you would be firmly attached to the seat. At the end of the 100 yards, my riding buddy and I pulled over and thanked the motorcycle gods and saints for our good luck. There actually is a Patron Saint that looks after motorcyclists.
In the spring, highway repair crews go out and pour tar into road cracks. These tar strips get very soft in the summer when the road gets hot, roughly the consistency of modeling clay. Eventually the car traffic wears them down, but until then they're very dangerous. Motorcyclists call them "road snakes." If you see them in a corner, steer around them: many motorcyclists have hit one in a corner and fallen down.
Highway lanes are very wide compared to a motorcycle. So, we get to pick where we are going to ride. A car driver will tell you to position yourself in the middle of the lane, because this is where they can see you in their rear-view mirror. This is the worst possible place to be, for several reasons.
In summary, you should be riding your bike in the tracks made by the car tires, about one to two feet away from the edge of the lanes. Unless your primary defense mechanism is to hope that the car drivers will see you and will save your life for you.
Carrying passengers effects the way a motorcycle handles. There's a lot more weight, and it's high up. Also, some passengers sit still, and some like to move around a lot. The movers can be quite disconcerting. If you've been riding for less than six months, you shouldn't carry a passenger at all. In almost all states the law is that your passenger must have a seat of their own, foot pegs, and a helmet. If you don't have all that stuff, don't do it. Small children should be belted to the driver - there's a section of this web site on carrying children. All passengers are considerably more comfortable if you have a back rest or a trunk with a built in back rest.
Cargo loads on a motorcycle can also cause problems. The best place to carry a load is on the passenger seat. Next best is on a luggage rack, a flat metal plate behind the passenger seat. Sometimes it's appealing to place a load on your gas tank and hold it between your arms: a bag of groceries, a dog, a small child. This is a really bad idea. Any cargo must be securely fastened to the motorcycle with bungee cords. Be careful not to block tail lights or turn signals or suspension parts. Make certain nothing interferes with your hands, arms, legs, feet, or the handlebars. Make sure nothing will hit the muffler. Many modern motorcycles have catalytic convertors in their mufflers; these get really hot. It's very distracting to be riding down the freeway and realize that your saddlebag or shoe is on fire.
For parallel parking at a curb, back into the curb so that your rear tire is touching the curb. If the street is on a hill, you may have to use a rather extreme angle to get your bike stable on the side stand. In most cities, there's an ordinance that says your motorcycle has to have one tire touching the curb to be legally parked. If you drive in and park with your front wheel touching, you're going to have to back your motorcycle out of the space up hill, as almost all streets are crowned. If you have a large heavy bike like a Harley, you're only going to make this mistake once.