Re: Ever get one of those knots.....
Rather than trying to diagnose the fine points of your problem I'll say this, too much false casting.
Questions: How long is the leader? How fine the tippet & how long? Wind blowing? Dry fly with large wings? Distance you are casting? Last but not least; how many false casts between when you pick up the fly and when you put it down?
It's been a long while since I had a tangle. I keep false casting to a minimum and always straiten my leaders prior to fishing. Even the leaders on my Spey rigs are straitened before I cast.