When you look at any period photographs of paratroopers in combat kit, they are always dirty, the kit is marked, stain, repaired in places and has been heavily worn. Assuming your not going to portray an fresh face trooper who is going to be based stateside and always be in training then you kit should reflect this.

So what is the best way to make your new uniform look like a battered, combat worm uniform... simple, follow these steps carefully.
1 - put on uniform correctly. Trousers on legs, jacket on torso.

2 - wear uniform at shows
3 - extra steps - to speed up the process, wear the uniform when doing gardening, working on your car, around a building site, when fixing the shed... in fact wearing it anywhere, anytime you're doing anything will age and wear it in naturally. 

Do not try and replicate dirt, wear an grim... it will happen naturally and look amazing when it does. Be patient!