Good morning, Pawel!
There are a few possibilities to explore here and I have to caution you that it really depends on the individual situation. I can only comment on what I have experienced personally in hopes that you or someone else can avoid my mistakes.
In some cases, the problem lies with the decals themselves. For instance, during the mid to late 1990's, Revell-Monogram issued a few kits with instructions to avoid using setting solutions and solvents. But, I'm a creature of habit and I ignored the warnings to go about business as usual. The solutions caused nothing but problems and I wound up having to purchase aftermarket decal sheets to replace what I had destroyed - an expensive lesson to learn.
I've also had wrinkling problems with older decals which are either excessively thick or old enough that the adhesives have begun to break down. I see this most often with the "vintage" kits I pick up off of e-Bay. What I suspect is happening in those cases is that as the setting solution evaporates, it is reacting with the old adhesives and the gases get trapped under the decal. In most cases, using a sharp knife or a pin to create a vent in the decal allows the gases to escape properly and a few more applications of solution seem to solve the problem.
Other mistakes I have made include cross-contamination on the bench. In the past, I've just reached for whatever brush is handy when I am applying decals and that's not always wise. Residual thinners and paints can react with the acetic acid and cause real headaches for me, so now I keep a set of those goofy Testor's brushes around just for decal work. I don't find them to be of much use with anything else, so they are just about perfect for me,
I avoid most problems by paying very close attention to my technique:
* Allow the gloss coat to dry fully - if I can still smell the stuff, it's not done curing and the gases cause problems with silvering and wrinkling down the road.
* Test things before committing - on just about every decal sheet, there is a manufacturer logo or other trivial lettering that will never be used. I find those perfect to experiment with before I start to go after the decals which will actually make it to the model. If I screw them up, who cares? At least I can adjust things before tackling the finished project, right?
* Don't oversoak the decal - no more than 10 seconds in lukewarm water, then I set it on a paper towel until the decal moves easily on the backing sheet. If I soak it too long, it compromises the adhesive and it just doesn't stick well. The more adhesive on the decal, the better.
* Light coats of setting solution - if I use too much, it messes with the adhesive or leaves strange streaks of chalky white residue behind, so I just use a pass or two of setting solution where I want the decal to go. Excess has to be wicked up immediately with a paper towel to prevent staining, but I also suspect that the less moisture I leave under the decal, the less chance I have of dealing with trapped air and gases as things evaporate.
* I have to be certain to put the decal exactly where I want it the first time around - if I play around too much with moving the decal, I wind up with problems.
* I improve my chances of avoiding wrinkles and problems by carefully working out the air pockets with a dampened cotton swab, taking care to pay close attention to recessed panel lines or areas where I have zimmerit or other irregular surfaces. The closer I can get things to settle in, the less chance there is later of me having to imagineer solutions to the problems I create.
* Let it dry completely before adding more solutions or solvents - when I first started using Micro Set and Sol, I was far too impatient and wanted to see immediate results, so I would use them liberally and often one right after the other in that quest for instant gratification. Not a smart thing to do... Just like with the gloss coat, if I can smell it, the stuff is not fully cured. It needs to be allowed to dry fully before moving forward. Now that I have learned a bit of patience, the Micro Set is normally all that I need to use and the Micro Sol is only pulled out in those cases where a decal is being particularly stubborn. Walther's Solvaset is the last resort for me because it runs so hot.
Anyhow, that's what works for me, Pawel. I hope it helps!