This is purely from my experience. When you first start shooting pool, you must understand your stroke is the key to controlling that rock (cueball). It is also important in aiming, because if you have a bad or crooked stroke, you will not see consistent results. Now the first thing you should do to straighten that stroke out and to keep it consistent. Get a beer bottle cleaned out and empty. Find a table in your house, ie. dining table. place it on the table if front of you and get into a stance (with your cue) as if you were going to shoot through the mouth of the beer bottle as you would stroke through the cue ball. Now keep in mind, you have to stroke through the mouth of the beer bottle without touching the rim. It has to be a nice glide in and out. You don't want to force it in. You want to swing the cue back in forth like a pendelum. there is no force on pendelum, just a nice swing. If you do this everyday for about two weeks i believe you will straighten out your stroke and also build up muscle memory which will help you be more consistent. Sorry I don't I have diagram to show. I'll try to post one up later.
