I have done this before and I used 5 gallons of water and less than just a drop or 2 of Palmolive.

The link below from the University of Colorado has a lot of information. Some key points: The usual concentration for insecticidal soap is 2%, I would go with a 1% solution (2 1/2 tbs per gallon) and I would rinse off the bush with pure water about half an hour after spraying, all to prevent leaf damage. I would use any liquid dish detergent, such as Joy or Palmolive. Soap solutions kill only insects that get hit by the spray directly, the dried soap residue on the leaves will not kill insects. Soap solutions kill aphids readily but I can't see a soap spray doing anything at all to thrips because thrips stay inside the blossoms where the spray won't contact them.

Here is a link that might be useful: Soap Insecticides