In a competition you cannot ask or tell a competitor the club you used to play  Rule 8-1

On the putting green  you cannot touch the green to show the line in which you intend to hit the ball Rule 8-2

On the putting green  you cannot repair spike marks from golf shoes until the hole is completed Rule 16-1

On the putting green  you cannot tap down lumps in the green apart from pitch marks You can brush away sand and loose soil. Rule 16-1

If when on the putting on the green your ball hits the flag it is a two stroke penalty Rule 17-3

If when on the putting on the green your ball hits another ball on the green it is a two stroke penalty Rule 19-5

You can remove loose twigs, branches and stones which is near your ball except when in a hazard, but if the ball moves it is a penalty Rule 23-1

You can only remove stones from bunkers. Leaves, twigs and branches cannot be moved. Rule13-4

When playing from a hazard (water or bunker) you cannot ground your club or it is a two stroke penalty. You have to hover the club head near the ball and can only hit the ground when you make an attempt to strike the ball. Rule 13-4