Is a tummy tuck better to do before or after liposuction?

It's very common to have liposuction and a tummy tuck procedure at the same time. The tummy and flanks are both common areas to treat during a tummy tuck procedure. Liposuction is typically performed first, and then the tummy tuck procedure is performed. Consultation with your plastic surgeon will help determine which procedures are right for you. 

A tummy tuck will include thinning out the fat layer in front of the abdomen, so I assume you are considering lipo in other areas. Depending on how many areas and how much lipo, it is usually all done at the same time. There is no reason to have liposuction on the abdomen before having a tummy tuck.