How to increase my appetite?

Look at cookbooks or watch cooking and eating videos. Eat more nutrient-dense foods like fruits and vegetables. Don't fill yourself up with liquids too much. Exercise more often. If these things don't work or you've noticed this change in your appetite all of a sudden you may want to talk to your doctor so that they can rule out a more serious cause. 

exercise a bit to get your blood flowing to your muscles and organs, and dont skip meals. eat something every couple of hours, just something small is fine, your stomach needs to be working to keep an appetite. also drink water to get your system flowing good too. Just the basics really :)