passed pawns with Q+R

I think I know relatively well rook and pawn endings, but I just realized how hard it is with promoting pawns against a Queen and a Rook.

Take this game for example:

Now I don't know if it's my tecnique that sucks or if it is objectively hard to push passed pawns: the opponent can use a combination of blocking and threats to my king. Maybe I'm supposed to use threats against his king also?

I would like if somebody could share some tip/technique on similar situations (especially Q+R+single passed pawn vs Q+R)...are there some common methods or is it just a matter of calculation?

Queens off the board is half the battle. As qg3, qxq,k/pxq,pb4,ra7,pb3,rxp,pb2 and he can't stop the p. Queens om board W/ rooks create many drawing opp.