I've become strangely good at solving this problem. What I do is kinda use one thumb as a blockade on a corner, then instead of sticking it, use the other thumb to establish about half a cm of a straight line, just to make sure the alignment is correct, and then I roll my thumbs upwards as to make sure I don't form air bubbles.
Oh, and @jokur_and_batmon pointed something else important out I make sure of, I make sure my hands are not wet or oily, my hands tend to produce more oil when building; perhaps because moving fingers so much.
My dad never let me put the stickers on. I would beg to because they were my favorite, but he said "We have to put it on perfectly." He's always been a perfectionist, but he's also always been slightly annoying.
Hmmm... I'll try that with a sticker I can afford the loss of; to test it against my own thumbs. I do see how that would vastly help with positioning, but would that compromise how long it would stay stuck? Some of the old stickers are starting to peel; my LEGO Ferrari, which is like a decade old, is what immediately came to mind. I've started ripping random pieces off of it, so it's no longer on display and I honestly don't care about those stickers anymore, but it would be a good thing to know.
Oh, and @jokur_and_batmon pointed something else important out I make sure of, I make sure my hands are not wet or oily, my hands tend to produce more oil when building; perhaps because moving fingers so much.