When asking about pruning you cant really just ask how should i prune myplants, because it depends on how you want your plants to grow.
If you are looking to split the top off into two or more colas then you would want to try topping or Fimming, topping is cutting off the top of your plant, fimming is much the same, but it all about where you cut. Fimming involves cutting through the node in just the right place

You should probably wait until your plant is at the v least 3(5?) nodes tall (i.e. there are 3/5 sets of stems coming off the main stem). If you do it right you can get so many little(not that little

) colas, check out me thread in indoor budshots i was well pleased with the results.
Some people try to get more light for their air buds (the littlens down the bottom) by cutting of the larger leaves (sun) on the top, dont really agree with this especially if u r in budding - the sun leaves are well important for energy, the alternative is to remove these lower branches all together before budding.
Obviously if u are a new grower you wont know which are gonna be air buds and which arent but after a single grow its not too hard).
If you want to grow short plants, you can keep cutting back the tops of your plants at nodes, creating more and more internodes. The plants ive got at the moment had a huge difference in height when i got them, so i had to cut back the larger two for a month or so and the internodal distance is tiny

Another alternative to all tis hacking and cutting is training, havent tried this but as i understand it you either tie the plant down or bend it in and out of a net or weigh down branches to direct the growth.
Another alternative you might want to consider especially if its ur first grow is doing nothing at all

If in doubt post a few piccys b4 u chop and we'll help u mutilate ur babys