A couple of thoughts on SOHP.
It is essential to develop great technique. There are a lot of lifts where having excellent technique is certainly a plus, but not essential to progress, ie you can just keep getting stronger with less than optimal technique. I have found that not having excellent technique will stall more guys than anything else and that is why you will often see a lot of guys that are stuck in the 200-225 range or so--it does not mean their technique is bad, but it may indicate that it ie less than optimal.
As was mentioned earlier, doing full body core type work is very important, the Overhead squat is a perfect adjunct move for the SOHP ( and just about everything else)
You may want to consider taking a block of time, say 4-6 weeks and really focusing on the OHP, not that you eliminate everything else, but you start every workout with OHP, then assistance moves, then do you normal workout, you can do this say twice a year or even three times a year if the stretch of time is shorter ( say 2-3 weeks) and this will often give you a decent bump in your poundages. When I was in the Navy, we did two patrols a year, which lasted about 75 days and before we went out, we would spend 30 days in port getting the boat ready--it was a grueling schedule and we often did not get off from work until 8pm at night if at all. I would go to the base gym and really did not have the energy to do complete workouts, so I would do an hours worth of presses and related work. I would do this 3 times a week for the 30 days and at the end of the month would always be stronger in the SOHP, even though I had been using less than optimal poundages during the training. The gym was always quiet and empty late at night and it was a perfect time to focus and work on my technique. I was there late one night and another guy came into the gym and ended up doing presses with me and then also some front squats---this was none other than NBA legend, David Robinson, who was fulfulling his military duty at the base.
An exercise that I have often described in the past is to take about 95% of your best OHP and get in the power rack--set the pins to a point where they are about 4-5 inches ( depends on your height) below where the bar would be if you were standing upright, with locked legs and the bar was rack across your shoulders. Get under the under the bar and do a modified push press driving up as hard as possible and try to get the bar just above your head, then slowly lower it with a 6 count. Rack the bar and repeat for 6 reps,,this is absolutely brutal--you wil likely need spotters, not so much for the safety aspect, but to "talk" ( ie, scream at you) through it. This exercise took my OHP from 275 to about 340 in less than six months.
Keith