I'm no expert, but you will need to do some research. Different preservatives are for different products. Some work better at low pH for lotions and creams and some at high pH, for shampoos and body washes.
I find that Phenoserve - it may be called Phenonip in the US, is a great all round preservative for all my lotions and creams. It's broad spectrum and is only used at about .75%.
It depends what you're putting in your products. If you're using lots of herbal or fruit extracts, you'll need to preserve the product carefully as these are prone to going moldy quickly.
Go to your fav supplier and search their website for the info you need.