AP Calculus is a hard class, and it relies on a firm basis in, pretty much, all math prior to calculus if you want a chance in hell of passing.
So, before even taking the class, check out some of this:
Its a GRE Math guide, but its helpful, giving a pretty basic overview on algebra through pre-calc.
Special Angles Chart – Trig is, sadly, a part of calculus, knowing this will make life SO MUCH EASIER.
Now we can start on Calculus.
The two tools above are online calculator and help sites for when a problem has you stumped. Figuring out what your doing wrong until it whats right clicks in your brain is like, 90% of this class.
Assuming you survived the class, you need to study for the AP test. The two links below are a pretty comprehensive overview.
Calculus Formula Cheat Sheet – MEMORIZE THIS
Sorry this guide is so short. calculus isn’t really something you can learn or cram in a month, and not really something that can be studied online.
But hopefully this helps a little.