If your aiming to Powertrain them to a specific Quality or lvl, then you need to buy green boosters (that is, if your low on them) and train them until they reach a * or **. Otherwise, it´s no big deal/or use to do that since they gain only +5% every 3hours.
About the bonuses, I set my bonuses to: CUP (100%), CL (80%) League (60%) ... Then the last two weeks or week I increase my bonuse for the league to 80% or 100% (depending on the table situation).