In a competition you cannot ask or tell a competitor the club you used to play  

On the putting green  you cannot touch the green to show the line in which you intend to hit the ball

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

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

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

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

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

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

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.