+ 1 on the Krylon Paint. A couple of us from Indiana have used it and it is great. It is going on a couple of years now, and still looks good. I read somewhere to use old magazine pages between the flares and jeep to keep overspray off vehicle. It worked really well. I used old JP issues.....lol
All Things Good in Life are Round....Breasts, Donuts and Headlights!
TJ flares already have a rough texture (non rubicon/sahara) so the paint bonds easily. All that is required is a good cleaning with soap/water.
And the TJ flares are a PITA to remove. Like posted above just use newspaper/magazines and tape everything up really well and paint inside or on a calm day.
Take your time, spray light coats with the Krylon Fusion and allow paint to dry for a couple of hours before going back and applying the 2nd coat. You will be amazed at how fast Krylon Fusion (and other plastic paints) dry, but for the best results you still need to be 110% sure it is dry.
You can also use a heat gun or torch to heat the plastic back to semi-gloss. Of course you would want to take them off first. The only thing that sucks about taking them off is removing the christmas tree fasteners on the rear wheel wells, so you would want to cut or drill the old fasteners off and then use new fasteners that you can get at any auto parts store.
There is a write-up somewhere on here about the heat.