I need one commit from a long branch, not the rest

git cherry-pick <sha> is the direct answer, but check whether the commit depends on earlier ones first. If it does, the conflict you get is real information: the change was never independent, and copying it alone will compile but misbehave.

It gets easier, not harder. A fair share of the difficulty is coordination, and that disappears. What remains is remembering your own decisions, which is what writing them down is for.