[bigc]

How do I know what reaction is going to result in a precipitate?

[enahs]

Write out the balanced equation.
Does it form a solid that is insoluble in water?

Pretty much at your level and the type of material you will be questions on, this means memorizing your soluble/insoluble chart in your book.

I highly recommend memorizing it by doing practice problems, not just trying to memorize it straight up.