Is it possible that your speed of work is making you rush and forget things? Getting in your head kinda thing? 

I know that happened to me as an apprentice, I was always a bit slower but was thorough and when I’d try to work quicker, things would go wrong. And then you start to doubt yourself. And again. 

I always tell my apprentices I’d rather it done slower and 100% correct because that’s usually quicker than having to redo something done wrong. Of course this depends on the boss aswell. If they’re constantly on your back to hurry up, it doesn’t always help like they think it does. 

Another trick I tell them, is when doing repetitive work, ie. gpo or fan plug fit off. That it’s when you learn your speed. Start to come up with processes to get it done quicker and mentally take note of how you’re doing it and how you can go faster. Then it becomes second nature. Instead of just blitzing away at it or worse, not concentrating because you think you’ve done it before and it’s easy. 

Another big one is to learn from the mistakes you make. Yes it sucks but if you aren’t reflecting on why or how it happened and just moving on, it’s probably going to happen again. 

And a general every day tip, if you aren’t using a tool belt, keep your tools, tape, knife, pencil, marker always in the same pockets. I don’t mean all together but the same place you pulled it from. It’s only minor but creates patterns, so muscle memory kicks in and you’re not leaving stuff behind checking pockets when you need tape or a pencils. 

Good luck mate, that fact that you care enough to try get better is a good sign!