I have got an awesome little chart here that I got from a class I took during my first trip to Japan. I have internalized the teachings in it and have been a better Japanese student because of it. By all means check it out and see if it can aid you! If you use the Hepburn system, this is a flawless way to get that verb to say what you want it to!

Yes, it is a bit crumpled, but that is because it is like an old treasure map, incessantly perused by many in pursuit of its promised riches.