I love the foam roller, and credit it as a large part of being injury free over the last year while training 14-20 hours a week. Here the protocol that I use, with a bit of rationale behind each point:
Pre-Workout: Foam roll the glutes for about 1 minute on each side as to “wake them up” and hit big insertion points (e.g., ITB, Hamstring). If anything else is tight, I will roll it, but very lightly, and no more than 8-12 rolls over the spot. Don’t want to go to heavy as to create damage before a workout.
Post-Workout: Only if something is noticeably tight, and then I will hit it for about a minute, but that’s it.
Foam Rolling Sessions: About twice a week, I foam roll for a good 20-30 minutes. These are the sessions where I really go at things hard and try to work out any adhesions and/or other issues I am having. I try to do these sessions heading into an off day or active-recovery day.
General Rationale: Foam rolling heavily can take a toll on the body, and should almost be treated like deep-tissue massage work if you do it right. For me, anything more than 2x a week is counter-productive. That said, hitting the glutes before every workout will help you avoid common problems with the hamstring and ITB, and keeping the time low won’t add any breakdown to the body, and, it’s a lot more realistic to foam roll for 2-5 minutes everyday vs. 20 minutes everyday.
That’s what works for me. Every body is different, but as guiding principles, I would separate the “purpose” of a session for really getting in there (don’t expect to train hard right after this and don’t do this too often) versus just waking and warming things up.