decal technique help please

Same here after 60+ years of modeling.  With the ability now to make inkjet decals, I now scan every decal sheet before beginning decal application. That way I can hopefully remake any I ruin.  This has saved me a lot of grief in severa builds lately.

Biggest problem I find with new decals is how thin the film is from some mfgs!  They look great, but way too easy to have them fold back upon themselves, and I can't get them back unfurled!

Heck, I still make decal errors after 30ish years of model building!! Practice, practice, practice!!

You just need to keep practicing on a glossy surface.  I've watched many how-to videos and read articles, but I've learned almost everything about decaling from my errors.  

I'm not familiar with the Vallejo System,but the key to getting decals to look realistic is a good gloss coat,this prevents the decal from silvering,allowing the film to show.I use Micro Set and Micro Sol,probably the equivelants of what you have.i apply the decal over the gloss coat with water,then apply a little of the set,if it need to go over raised surfaces or down into detail,then I apply the Sol which is stronger.after everything dries,then cover the decal with another shot of clear coat,either flat or gloss,whatever your final finish will be,this protects the decal from the weathering process.

There a lot of good videos on YouTube on how to install decals.