Hi!
I responded to a post yesterday about which kits could help gain you the skills needed. I had mentioned certain company's products. I stand by that. Now there's another aspect as well. Working with Plastic can be confusing for some.Why? Well, look at it this way, you are trying to figure out how to work with this stuff and in some cases it will be soft or again, it may be Brittle.
Well, now there's a thought. Soft or Brittle? In Plastic there are some instances where you can take a big sprue(Or tree) of parts and bend the Sprue(With the parts on it )almost double before it reluctantly breaks. This is of course soft material. The other just snaps in two as soon as you try to bend it. This affects how you remove the parts(What kind or sprue cutter) and Sanding techniques as well as sanding materials.
I have found the sanding Medium on Mylar to be usless over the long haul.Regular Wet or Dry(Quality is a must here) Sandpaper is the best. Most of the "Made in China" or elswhere perform way different than 3-Ms products. Plus some are just to heavy for use on models. Now I hadn sand a lot.Why? I have gained by experience both with wood and plastic a "Feel" for the surface as I sand in under a flow of water or a light blast of air.
These things come with time. Time spent practicing with these models that don't seem to mind your machinations on them. Some are very forgiving. Some can be awful to work. Again, the nature of the product. You learn as you go. Be patient,I didn't learn it overnight either. To get to the level I am now, took many, many years. But that's okay,because, it's all been fun.
The real truth is this, be Patient, the skills will come, Sometimes life gets in the way, but that's okay! You Will Not Fail if You're Patient, first and foremost!! You would have expired because of laughter at my early attempts! Good Luck and Don't give up. If you have a question Ask Here on the Forums and you may find the answer!