Do the Basics of Skateboarding

You bought a skateboard. You left it in the shed for a year. Wish you could skateboard? This is to help.

Steps

Get on your board while on carpet. If you're not allowed to stand on your board in the house try in the grass. While holding onto something get used to how the board feels and everything.
Once familiar with the board, try standing on pavement without holding anything, put something nearby just in case you fall.
Then, decide what your feet positioning is. Skating with your left foot in front is called regular. Skating with your right foot in front is called goofy. Try standing both feet together and stepping forward. Which ever foot you step forward with is most likely your lead foot. Try riding with this foot forward; however, feel free to switch until you are comfortable.
Once you get your feet positioning, try to find a small hill to ride down. Some driveways are slanted slightly, leading to grass. This is a great way to practice.
After that, try turning the board. Leaning to a side can turn the board, but you can also apply slight pressure against the tail, or the back concave part of the board. The board's front wheels will lift off, this is called a manual. Don't stay in that position to long. Once the wheels are off, immediately turn your legs to the left or right to turn.
Try riding at faster speeds after that.
Next try riding over bumps and off ledges this will help build your core balance for doing trick in the future.
Once comfortable with board, you can start doing tricks.

Make sure to have good shoes. Obviously nothing with a heel, and nothing too heavy. Lightweight, covered skate shoes are ideal.
Never try to do tricks as soon as you start because you can get hurt badly and then you won't be able to skate for a while.
Keep your knees bent, it helps you to not fall and to go higher when you do tricks
Don't expect to do this overnight, so persevere until you get it right.
Don't be scared, as long as you prepare by wearing a helmet and pads you shouldn't get hurt too badly until you start doing more complicated stuff.
You can also learn tricks in a skate park. Watch what other people do, but make sure not to get hurt trying it yourself!
When you have learnt all of these, start learning how to do an ollie and then learn some new tricks such as the Kickflip or the 50-50 Grind.
Keep trying and don't give up!