1. It's just your habits, if you don't like them, then you'll just have to change them over time. Like I also used like to keep items even if they're helpful, but then I just felt like using them would be better, so next chapter I played, I just brought out the unused items that could be useful (like staves that don't heal HP but can be used to train staff users) and I just used them up. Also, when you get rather close to the end of the game, use any weapon you want/can or else you'll be stuck with normal bad weapons (assuming you're like that).
2. Try to un-equip weapons from your "overpowered" (since from what I see, you play FE10 a lot) units and just let them take hits instead of actually fighting.
3. Try to set goals for turn counts, think more of the objective than of anything else.
5. That's kinda why I don't feel like playing FE10 on hard mode. xD But if you want to play hard mode, you have to accept it and eventually you won't even need to count and know how far enemies reach.
6. You could try taking breaks if you're not feeling concentrated at times.
I hope I helped a bit, have fun! :P