Details matter. Hole placement, angles at attachment points, relief for the hand are important.
Sand the edges well. I do 120 and 220. Then I buff with a green scrubby.
If you have to soften the kydex to adjust, use 1 second bursts on the area. 1 second on, one off until you can shape it.
Never heat around a drilled hole. It will warp.
Use something flat about 1/4" thick to mold the area in front of the trigger guard and under the muzzle. This will help you keep the lines straight.
You can buy rubber spacers off holstersmith.com or holsterbuilder.com. Automotive fuel line hose works as a retention part.
Use nylon washers under the straps to let the strap sit on the pants. No space between the kydex and strap means the waistband doesn't get up there.
1 1/2" stick on velcro fuzz increases comfort.
Paint sticks can be cut and sanded to make shapes to make relief for Chicago Screw Posts to attach straps and Ulticlips.
You can score kydex with a knife and bend it until it breaks. You can trim by scoring and using a needle nosed pliers to break off small areas that can't be done with fingers.
A rag on a dowel takes away kydex dust and helps keep your gun clean.
Cover your gun in painters tape. Attach molding pieces to it with tape.
Heat the kydex to 325 to 350. Avoid burning it by watching it at all times.
This picture shows burned kydex: