I'll second what NVS mentioned above, decals apply best to a glossy surface. Also, are you using just Micro Sol, or are you using Micro Set as well?
I've been building models since I was young, and the system I've settled on for decals is as follows:
-Paint model, allow to fully dry.
-If matte paint, overcoat with glosscote. An alternative is to paint with gloss paints, then dull coat it later. Allow to dry.
-Apply decals. First use Micro Set (blue bottle). While the decal is soaking in water (I use distilled water since I have hard water where I live), apply a small amount of Micro Set to where you plan to place the decal. Slide the decal into position, the idea is you are placing the decal onto an area already wet with Micro Set.
-When you have the decal in position and snugged down, apply a small amount of Micro Sol on top and around the edges of the decal. Micro Sol will soften the decal and help it conform to the surface. Try not to touch the decal after this, as especially with thin decals, they can be easily torn when softened. If the decal wrinkles slightly during this step, just leave it. As it dries, it should shrink back to the surface.
-Suggest using quality brushes for this, I have two dedicated sable paint brushes I use only for decal work, one for Set and one for Sol.
-After decals are fully dry, overcoat with gloss coat again. The idea is to have decals sandwiched between gloss coats, which will help them blend in better to the surface. Thick decals may require multiple gloss coats.
-If a matte finish is desired, overcoat with dull coat.
-Weather model.
-Apply final overcoat (dull or gloss as desired).
Yes, that's a lot of steps, but will really produce the best decals on your models. Also, I would not weather your model until after applying decals. Weathering is generally done on top of a gloss or dull coat.
I've never sanded decals, not sure why you wanted to do that? All sanding would do is remove some of the decal, and as you saw, greatly increase the chance of tearing or cracking it. If you want to fade or weather decals, I would do it with paint (drybrushing, airbrushing, color wash), pastels, or even colored pencils.