Deciding when to float the flop in Texas Hold'em involves considering a combination of factors, including the board texture, your opponent's aggression level and betting pattern, the strength of your hand, and your table image. You should look for situations where the flop is likely to have missed your opponent's range, and where you have a good chance of improving to a strong hand on the turn. Additionally, floating can be an effective play when you're facing an aggressive opponent who is likely to continuation bet, as it allows you to control the pot and gain more information about their hand.