Apologies in advance - i geeked out. Do some practice swings before if you can. Stand with feet shoulder width apart and bend your knees slightly. Align the ball up to the center of your stance. Line your body perpendicular to where your trying to get the ball. Try to keep your left arm straight and hold the putter a little off the ground. This is your guiding arm, right arm can bend slightly while you swing. Keep you right arm loose. Make the front of your putter parallel to where you want it to go. Always keep your eye on the ball. You want to aim at hitting the center of the ball. If you hit it above or under center it’ll cause spin and mess up. Make your putter swing like a little arch when you hit the ball. Follow through as far as you swing back, unless you need more power (like when putting up inclines). Strategize where you want your ball to go. Use geometry to your advantage, you can knock the ball off any surface so use those angles. Take into account unevenness of the green. If it goes up a little bit you’ll have to hit the ball a little harder, if it goes down it will go farther and faster than you expect. Sorry if this is too much, or basic stuff you already knew! I hope it helps! Fwiw I use to take golf lessons, and was an extremely competitive put-putter as a child. Hahaha