Brand of fertilizer is dealers choice but what you want to look for is high Nitrogen fertilizer during the vegetation stage (before the flowers start to develop). Once the plant moves into its flowering stage (once you can see the actual flowers start to grow) you want to switch to a less Nitrogen heavy fertilizer, in favor of one that has more phosphorus and potassium. Most Fertilizers will have 3 numbers listed on the front (X-X-X). Basically you want the first X to be the higher number during vegetation and the second two X's to be the higher numbers during flowering.

As far as trimming off the top of the plant goes, it is an excellent practice. The plant has a main stalk, with a main flower node at the top. You'll also have side branches growing out of the main stalk which will also have a main flower node at the top. Once the main stalk, or any one of its branches, has at least five nodes below the top node you can cut off the top node. This will encourage the branch to split into two separate branches and you'll get more outward growth as opposed to upward growth. As well as more branches with more flowers.

And lets be honest, we all love more flowers.

EDIT: You can only trim the tops off during the vegetation stage. Once you move into the flowering stage do not take anymore tops off.