Yes, I use decals a lot …
I cut them very close so there is little film around the actual insignia, words, etc.
I soak them in water.
Use a brush to slide them on where I want them to go.
I use a dull Exacto knife to place them exactly where I want on the model.
I use a light touch of Micor-Sol to get the decal to mold to the location on the model.
After it thoroughly dries. I use a brush on clear flat. Army Painter Anti-shine Matt Varnish or AK Interactive Ultra Matt Varnish.
The next day spray clear flat lightly on the entire model. I like Tamiya's Clear Flat or Testor's Dull Cote[if you can find it?].
Hope that helps … Like anything else … the more you do it the better you get at it.