There are a ton of websites describing it online - I'm sure this one covers the basics:
oilpulling.com/ - it's really simple, you literally just swish oil (I use sesame) around in your mouth for 20 minutes (I do it first thing in the morning - supposedly it's best on an empty stomach) and then spit it out in the toilet or garbage, NOT the sink because it might clog things up. It's used in Ayurvedic medicine, it stimulates the detox pathways via the big vein under your tongue - I've been doing it every day for the last couple of weeks and I really do think it's helping! Contrast showers are another little thing you can do easily every day - you just switch back and forth between hot and cold water a few times at the end of your shower, it helps your body regulate itself. All the little things really do add up and have a cumulative effect, and whatever you can incorporate into your daily routine is always the easiest to stick with.