When you are told to 'swim good', it usually means that the engagement ahead of you is going to be tough.
Tracing back the genesis of the phrase, you go back
to the days of 1700s slavery in the USA, where it was used between slaves to bless another person. 'Swim good' is most likely an ode
to the days when slaves were
transported on ships, if you were to jump off, you would have to 'swim good' to make it any close to shore.