As others have already said, the biggest mistake people make is over throttling. Tendency when people get nervous is to over react or in this case over throttle. Speed is your biggest enemy when docking. Best thing to do is think things through in advance. Wind direction usually more than tide is a big factor, unless your slip is on the main river in which case tide might be the over riding factor. Slips inside a marina wind direction is more a factor since there's very little current once inside. Either way, think it through before leaving and coming back in. Predominant wind direction during the summer in our area in the afternoon is SE, understand what that means in docking your boat. If not SE, then it's typically W, understand what that means. If you have it down in your mind what you have to do then it's just a matter of executing. And DON'T over power the boat, nice and easy and as someone pointed out, bump it in and out. It's not rocket science, just trial and error but know in advance what you want to do before putting yourself in that position. Fwiw there's nothing wrong with asking someone for help the first few times you try, nothing beats experience and it will shorten the learning curve and take some "error" out of trial and error!