What can I do in 3 weeks to get in better shape and look healthier?

I know there are a gazillion similar ?s out there like this, but I'd like some personal tips or suggestion. I have a reunion of sorts in 3 weeks. People I haven't seen in 15 to 20 years agghhh. I am not over weight, but am in the cusp of almost being there. I am 5'8 and 155 to 160. I know it will be impossible to lose a great amount of weight, but would love for my jeans that used to fit perfectly to not be tight by then. I also want to know of any foods or regimens that are helpful for a healthy look. I am a smoker and quit today... for real. I think with this upcoming event I can really do it. Anyway I would appreciate any advice in getting in shape and having a noticable healthier skin. Thanks guys.