How do you deal with the frustration of missing easy pots?

A bit of background. I used to play when I was a teenager, I had a few coaching sessions with a coach called Brian Cox, great coach and he helped me improve greatly.
I stopped playing when I was 19 I think, and have just recently started playing again (27) after getting contact lenses. I am struggling to string a few balls together now. Had a session a few weeks back with a different coach from my area, he tweaked a lot in my approach and I feel that it's a lot steadier now, cue going straighter etc..
Anyway, using the routines I was given by Pete, I can pot a few decent balls together but I'm let down by either my positional play or simply missing the easier pots. I start to miss a few, get annoyed and just go to pieces really, missing straight balls, blacks off the spot etc.. It's really doing my head in that I can't seem to play like I used to, and I think a lot of it is down to me missing and then getting distracted by being peed off. Don't get me wrong, I was never a half decent player, 25-30s average break, 48 highest. Any advice from anybody regarding the temper please?

How do you deal with the frustration of missing easy pots?