You should have a "clear" set that is trasnfer tape... you peel the clear tpae off the backing, and apply it to the top of the lettering decals. Press it down firmly...

When you peel it off again, the letters should stick to the clear tape....

THEN you apply it to the plane... and press tight.... then peel the tapeoff... the decals should stick to the plane because the clear tape adhesive is less powerful than that of the decals.

Of course you tape the WHOLE decla... not just a letter or two... so youcna apply the whole word in one pass and they are aligned perfectly as cut...