working towards a one rep max

Hi all, I'd really appreciate some advice on how i'd go about working toward a one rep max lift on my squat, dead and bench, i train twice a week for 40-50 minutes, warm up, bent over bb rows 2x8, bb bench 2x8 and squat 1x20 then abs. On the other day i military press 2x8, weighted chins 2x8 and 1x15 deads then abs. I do not always get all my reps since i try to increase the weight if i do and some days i feel better than others. i dont know if this is a great routine but i always leave the session exhausted and i have made gains on the weights i lift. I train muay thai and boxing on other nights but am not competitve since i have the coordination of someone in the middle of an ether binge. I'm 5'11" and 12st 5lbs. squat 20 x 90 dead 15x130 and bence 2x8x85. Could someone help me with a routine to work towards less volume and more weight? Thanks in advance and i apologise if this is a stupid request or covering old ground, cheers ladies and gentlemen.

I gave my bodyweight in imperial but the weight lifting is kgs!