Too many things to say... I appreciate everything said so far so I'm hesitant to give any more info. Already so much has been said that I'm not sure I need any more tips. Just for your interests though, it’s a 130L Exocet board, I’m 70kg, 5.8m2 sail, big fin, I don’t know how big but I’m sure it’s not a problem.
After reading the comments I don’t think I’m really doing much wrong except for going out when it’s too windy. I’m probably loosing most of my ground when I fall in.

When I find myself downwind I often think maybe I should go out again to make some ground up, then I look at my red hands and feel my sore lower back and decide that the walk is probably an easier option.

On low wind days it's never a problem.
Re: planing, yes when I get going fast enough, same for feet in foot straps, although I rarely get going reliably fast enough for this.
Feel free to add more comments if you want, but I think I get the gist of it.
Cheers