Do mobility work at the end of your workout when your muscles are flushed with blood and your joints are well-lubricated. Just take a few minutes for these six simple mobility drills and stretches. You'll want to do each one for 10-30 seconds.
Sit way back on your heels and paste your ribs to your thighs to stretch out your lower back, hips, and groin.
Grab onto something solid if you need to and sink as deep as you can into a squat. Make subtle weight shifts from foot to foot and from heel to toe. Flex and extend your spine. Relax and let things open up.
Stand with one foot on a 45-degree angled platform or on the edge of a step if that's the best you've got. Shift your weight around your foot in a clockwise rotation for 2 or 3 rotations and then do the same counter-clockwise. The movement should be so subtle that someone watching would barely notice you're moving. This will be a big help to your ankle dorsiflexion mobility.
Your hip flexors, chronically shortened from too much sitting, will thank you. Dr. John Rusin coaches the best way to do it.
Using a box or other horizontal surface at about knee to mid-thigh height, place your leg on the box so that your lower leg is perpendicular to your torso. Lean over that leg and gently oscillate forward and back and right to left. This is simply incredible for hip mobility.
Grab a pull-up bar at about shoulder width, keep your shoulders down and back in a solidly packed position, and enjoy the vertebral decompression effects of just hanging around. Ideally, find the highest pull-up bar you can. Extend your entire body out nice and straight for the most benefit. If you're too tall or the bars in your gym are all too low, extend your legs out slightly in front of you with your feet just off the floor rather than tucking your feet behind you.