The focus is mostly on the piece your opponent just moved, and the piece you are moving. Most of the time, a blunder will involve one of those two pieces. Most of the rest of the time, a blunder will involve a discovered attack or not noticing that a piece was pinned to something more valuable.
Ways to lose your queen in one move mostly consist of:
You move your queen to a spot where it can simply be taken.
You move another piece which was pinned to your queen, allowing it to be taken.
Your opponent moved a piece which is now attacking your queen, and you ignore it.
Your opponent moved a piece which allowed another of his pieces to attack your queen, and you ignore it.
So that suggests a basic checklist of:
- Make sure the piece you're about to move can't be taken for free.
- Make sure the piece you're about to move isn't pinned to another piece.
- Look at what the piece your opponent just moved is attacking.
- Check if your opponent's move allowed another of his pieces to attack you.
Ways to lose your queen in two moves mostly consist of:
Your queen gets pinned.
Your queen gets skewered.
Your queen gets forked.
Your opponent plays a discovered check which also attacks your queen.
Your queen gets trapped.
So the slightly less basic version of the checklist makes sure that your move does not allow any pins, forks, skewers, discovered checks, or trapped pieces, and that your opponent's last move does not threaten any of those.
And you should, of course, always be watching out for checkmate. It doesn't matter if you lose your queen if the game is over.
This is not comprehensive - there are other ways to lose your queen fast. But it does check for some of the most common basic-level blunders.