Have your tweeters at ear-level (assuming your speakers have them).
Distance is dependant on the optimal soundstage your speakers produce, so you have to move them around and find out. Aiming them towards your ears means you hear them first (which might make it sound brighter). Aiming them past your ears towards the wall means you hear mostly the reflections.
I like having speakers widely spaced (about 6-8 feet apart) and the woofers aimed straight, passed my ears so its a bit more laid back.
The subwoofer should be between the two speakers. If you have two subwoofers (optimal), then put them right under each speaker. This way you get bass in phase rather than coming off-timing and possibly destroying other waves.