The best thing to after a workout is give your body the necessary nutrients to begin the recovery process.
After any strenuous training session, cortisol levels are elevated. If you're not familiar with cortisol, it is a stress hormone that can break down lean muscle tissue.
Think of cortisol as pac-man, going through and gobbling up the proteins that constitute your muscle cells.
Within 30-60 minutes following your workout, consume a meal rich in protein and simple carbohydrates.
Whey protein is a great option, as it absorbs incredibly fast and is high in amino acids. This will help reduce muscle breakdown and begin the rebuilding process.
Simple carbohydrates too are important. Like whey protein, they absorb incredibly fast and can blunt the effects of cortisol. They're also critical for replenishing the spent glycogen in your muscles, which further aids the recovery process.