Neck Adjustment
A common problem with electirc guitars is when the neck may be bowed in or out. This can happen in many different ways, but the most common comes from leaning the guitar against a wall or other object. Over time this can cause the neck to bow inward on itself and hurts the playing action further down on the neck.
The solution for this is to adjust the truss rod. Depending on the type of guitar you can adjust the truss rod that is in the center of your neck. Usually a hex wrench is needed for this task. Try adjusting the truss rod to improve bow of the neck. A little bow upward is ok. If you do not see a truss rod adjustment at the headstock it is most likely at the other end or butt of the neck. On some styles of guitars it is possible to adjust without taking the neck off of the guitar. But in most cases you will have to unbolt the neck from its neck pocket to adjust. If you would like to save your current strings, sometimes you can put a capo on the neck to save the strings. In some cases you will just need to take off the strings and adjust the neck. This is a trial and error process, but once your neck is adjusted properly, you will no doubt get a better sound and feel out of your guitar. Try small quarter turns of the nut to see what kind of response your getting. Remember that loosening the truss rod results in higher string action, and tightening it will give lower string action. The adjustment depends upon your style of play and how you like your string height on your guitar.
This is a simple solution that most people can fix without needing to take their guitar into a repair shop.

Bridge Adjustment
This is a very important thing you can do to simply make the play of your guitar easier, or to prevent notes from fretting out on the guitar (which is caused by the strings being to close to the neck).
The string action can be raise or lowered by adjusting the bridge. If you don't feel comfortable adjusting the bridge yourself try your local guitar dealer. They usually employ technicians to help with guitar modification. Basically the raise or lower your bridge adjust the screws on both sides of the bridge. This is another trial and error process so adjust the bridge a little at a time and test. If you adjust the bridge to low your guitar may fret out. This means that the strings are adjusted to low and give false tones when certain notes are depressed on the fretboard. Also if you go to high your action may make it more difficult to play chords on your guitar. So a little adjustment can go a long way.

Restringing
This should actually be dne when either a string breaks or also when strings "die". Strings may die over time because they will stretch and lose their tension. This causes the strings to come out of tune very easily and then it is time to replace them. For most guitars it is a fairly simple process.
You'll need to loosen and remove the old strings by unwinding the tuners and pulling the ball end of the strings out from the bottom of your tremelo. You may have to take off the back plate of the guitar to do this. Take your pack of New strings and Start with you low E string. Guide the string through the bottom of the tremelo so the ball end fits snug into it's pocket. Take the string all the way down make sure it's guided through the nut. Wrap the string around the tuner post and when you don't think you can wrap anymore then take the string through the hole in the tuner and over the strings. This should hold the string in place. Sometimes pliers can be used to help get a grip on the string and help pull it through the tuner hole. You may also want to purchase a string winder for changing strings to make it easier.