The absolute "safest" prespray would be to prespray with a dry cleaning solvent. This will actually dissolve many oils on the fabric before you clean it. More soils are oil based than some cleaners realize.
By using a dry cleaning solvent, you will not have things like shrinkage, water staining, colors bleeding, brown-out, etc. happen. (Of course, there are always rare exceptions to some of the above problems.)
The disadvantage to using a dry cleaning solvent is that you will be limited to dissolving light oil based soils only. Any water based soils will not be removed. For this, a water based prespray/detergent is necessary.
One more advantage to starting out with a dry solvent is you will be creating a moisture barrier. In other words, any wet cleaning procedures that may follow will not get the fabric as wet. So less concern about a really wet fabric browning, bleeding etc. and a shorter dry time.
This is probably the "safest" way to begin, next to getting proper training of course. Proper training will teach you what could possibly go wrong, and why. Then you will know what to do and what to never do.
Cleaning fabric can be a scary thing without a little knowledge.
Jose Smith