I am really bad at writing alot, so I will try and put some stuff in a nutshell for ya
Make sure she's eating kitten food now through when the kittens are weaned around 6 weeks. You will still want to keep her on kitten food until she is showing signs of good condition.
Designate a single room for her to stay in from now until the kittens are old enough to venture on thier own. You will want to create a box for her to have her kittens in. I like to use one of the large tupperware containers you can get at most stores. Put some nice towels or blankets in there to make it comfortable for her. If mom doesn't feel secure when she has her kittens, she can start moving them and hurt them on accident. It's best to keep it nice and quiet for her.
When it's getting close, you will notice that she's sleeping much more, eating lots less, and will get restless meaning she will probably get up and down alot and seem uncomfortable.
When it's time, you will see her contract just like people do. Once she starts to contract, it will be VERY soon. You just want to keep an eye on her for stress, or any problems. Generally they can give birth themselves, but sometimes can have problems. My suggestion for that would be to get a book to refrence incase you need it. Most large book stores have a section for cat care and have some good books on pregnant kitty's.