Exercise whenever you can. Anything that aids in general fitness should boost your circulation. When you work out, try both.
Cardiovascular training. Swimming, biking, running, playing sports, etc. Aerobic activity will improve heart and blood vessel function.
Strength training. Strength training (lifting weights) will help you build muscle, which in turn increases the effectiveness of cardiovascular and lymph circulation.
Every hour, get up and try 3 to 5 minutes' worth of stretching or small exercise. This is especially handy if you're at a desk all day and barely get a chance to walk around. Try doing little arm circles, touching your hands to your toes, kicking out your feet, or performing small, slow jumping jacks (enough to get you heart rate up).