Silver
I guess there are 2 approaches to the mental side of the game. The technical aspect "pre-shot stuff" and the "before, during and after your round" aspect. There's plenty of stuff on the former, but here's my view of the latter.
I have an incredibly busy schedule these days with work, family, DIY etc. I use golf as a way to relax. I only get one shot at it each week (during the Winter anyway) so I try and make the most of it, rain, hail or shine. That means preparation.
I've found a few things that "get to me" in golf. Running late, trying to find clubs, tees, etc. Having to run the kids to a club, 2 mins before my tee time etc. It always ends in disaster, usually even before I hit my opening tee shot.
What I have found to work is giving myself some preparation time. So on Saturday night, I get the clubs sorted out, clean shoes etc. On Sunday I get up 30 mins earlier and get down to the club to try and warm up, even if it is only on the putting green. I try and stretch and start thinking about the round. I look to see where the pins are, what way the wind is blowing etc. It all starts getting fed into "the computer". This all sounds anal but if I have all these things sorted out mentally I have less reason to collapse on the course and I don't have to think about it. I can just focus on the shot.
I also try and leave any mental baggage in the car park. If I'm having a bad time at work, at home etc. it has to stay there. Bringing it on the course implodes my game. I may as well just go for a long walk with the wife and kids otherwise. Hangovers are somewhat of an issue, but if the preparation is done, then it makes it easier just to swing a club.
But probably the biggest thing I have been able to do is to enjoy my game and not "beat myself up" too much. I am not a tour player, so I am going to hit a lot of bad shots. The fact that I do not practice 6 hours a day means I can accept this a lot easier. Why am I out playing? I enjoy the game, I love hitting a shot that comes off, I love competing and posting a score, but it is not my livelihood. So what if I hit a shank, yes, I get frustrated, but it's not the end of the world. This may sound defeatist but I have found that by "staying happy" it is amazing what a positive affect it will have on my game.
I no longer throw clubs, or get pissed off. I just accept it and move on. If I hitting the ball well, I can make back that shot, if I'm playing like crap, there's always another day. If it is the latter, I tend to try and hit various shots that are higher risk, just to try them out. I'm already practising for the next round.
So here's your goal for your next round. Set 90 as your score target but also give yourself a score out of 10 for preparation and a similar score for how much you enjoyed the game (regardless of score).
Track these scores along with your actual score and note the correlation. I'll bet that when you start breaking 90, both prep and enjoyment will be sky high.
Anyway, all this stuff is hurting my head.
Good luck.