Train your squats and pull in the weightroom too because that strength will better carry over to football, but combines test the bench for reps still, so you need to prepare. Honestly it isn't a strength test, but more of a strength endurance test. The best way to improve it is to practice it. I'd say if your 1RM is under 315 it will be closer to a strength test for you and getting a better bench will improve it. If your bench is over 315, 225 is an endurance weight for you and regardless of your strength increases, you just need to "practice" with 225 after a workout.
A little trick guys have done is to rep with 230 after a bench workout and when they test on 225 they get some extra reps. Also, hit a fairly heavy single during warm-ups and 225 will feel lighter and you'll get extra reps.
If you weigh under 200lbs, they will probably test you with 185 x reps, not 225. If you come in at 210, they'll test you at 225, but take that into account for sure. Also, what position do you play? Arena Ball will play you both ways. With your target weight, you sound like a receiver / D-Back....in that case a good bench for reps is always a bonus, but as far as physical attributes, coaches are more concerned with your speed, agility, and vertical.....and of course SKILLS. You could play FB/linebacker, in that case if you're a hell of an athlete who cares about your bench......if you're gonna use strength as an equalizer, a FB/LB is gonna need their 225 x reps to be 20 or better to get noticed....if the individual scouts care about it.
I have no clue as to your training background, but if it is more bodybuilding oriented, make sure your spotters aren't douche bags in training (they can't touch the bar or the reps aren't gonna count).
Other than that, box jumps, sprinting, and general stretching etc will help. Of course if you're blessed with explosive power and great "change of direction" speed, then you'll have an advantage.
When I was in HS, the first thing recruiters asked was if I could dunk a basketball, the second was what was my 40 time, the third was how much I could power clean, the 4th was how much I would squat. So....that should tell you how much the bench is worth....but like I said, combines love it. The NFL loves it because Joe Public can relate and it attracts fans to the combine, other leagues use it because "the NFL uses it"....most colleges with good S and C coaches test upper body strength with a 1 rep max on either bench or incline, then something standing and overhead like a push press or a jerk (which most college football players turn into a jerk press anyway, lol).
Have you ever played ball before? Arena ball is a FAR cry from semi-pro, meaning arena is the real deal....even Arena 2 rosters are made up of mostly former Div 1 and 1-AA players. Not to discourage, but just so you know to prepare as Arena ball is not a softball league full of weekend warriors.
Good luck, and post some updates.