I'm fighting soon and my bjj school doesn't do much mma. I have good takedowns and strong passing. I'm thinking one area that is overlooked by bjj guys is top control from the turtle on someone who just wants to stand back up. As bjj gets more "sporty" over the years what other positions are often overlooked for fighting? 
One thing that is generally forgotten in pure bjj but crops up a lot in mma is keeping people down - bjj players often accept the bottom position to play guard while standing-centric mma fighters will pop right up from anything to a takedown to a loose side control transition.
Learning how to keep someone who didn't want to be down down as probably my biggest bjj -> mma adaption 
vidavaletudo - One thing that is generally forgotten in pure bjj but crops up a lot in mma is keeping people down - bjj players often accept the bottom position to play guard while standing-centric mma fighters will pop right up from anything to a takedown to a loose side control transition.
Learning how to keep someone who didn't want to be down down as probably my biggest bjj -> mma adaption
Agreed, that's what has helped guys like Maia, Jacare and even Gunner Nelson become so successful and racked up wins over super tough opponents compared to other high level BB's who haven't done as well in mma. More often then not once any of those guys mentioned get you down you are going to stuck down there for a while or it will be a hell of an attrition for you to finally stand up.
vidavaletudo - One thing that is generally forgotten in pure bjj but crops up a lot in mma is keeping people down - bjj players often accept the bottom position to play guard while standing-centric mma fighters will pop right up from anything to a takedown to a loose side control transition.Mega big time. Bjj really is practiced in a bubble. The counter to a lot of bjj is to just stand up.
Learning how to keep someone who didn't want to be down down as probably my biggest bjj -> mma adaption
Stand-ups from the bottom (guard, half guard and bottom of side control)
wrestling rides from the turtle
Also escapes and reversals from the head arm judo throw and from scarf hold position on the ground
So your fighting soon and don't train mms? Sorry to be negative, but sounds like a bad idea.
Controlling Arms and Posture from Guard.- So overhook guard or sitting up over the shoulder kind of like the Kimura-Hip Bump-Switch type position (Watch old school Cub Swanson fights for this.)
Standing up near a cage
Getting on your side to escape from bottom positions
Then all of that in reverse so getting posture, Holding someone against or down near the cage, and keeping your opponent flat.
Take downs from the clinch also a must.
Good luck!!
Triple_B - So your fighting soon and don't train mms? Sorry to be negative, but sounds like a bad idea.Yeah I train either bjj or kickboxing every day and have a wrestling background. Just trying to consider the gaps.
Focus on pace.
In strict BJJ you can play a very patient game. MMA requires proactive pressuring. Be aggressive.
Controlling from top half guard is great for mma. bjj guys will often accept the bottom position, but when you roll against a good fighter you realize real fucking quick how bad the bottom can be. I would worry less about submissions and more about position and control. You don't need to worry about passing to side or mount as much, but you probably already know this.
If you are on bottom work on escaping and just getting up. That's something that gets forgotten in BJJ. BJJ guys will often just stay on the ground when there are ample opportunities to simply stand up.
as mentioned....keep them down with aggressive, pressuring style and not be accepting/seeking of bottom guard out of habit. likewise mentioned controlling arms and posture, and space.....on bottom,you either tight or far, you can't play a middle range with striking. so if you cant get the control and posture GTFO and dont stay there.
IME, use striking judiciously. As Relson would say "is de spice". I see a lot of people flailing when using strikes within grappling structure. control, pin, strike, hepeat.
imo, if you at a school that doesnt really have this kind of experience training jiujitsu in this manner, you kinda screwed because there are many things that make up a vale tudo type game that is then modified for an mma ruleset.
Wall/cage wrestling. If you are mainly a wrestler or jiu jitsu guy you need to have wall wrestling fitness, technique or at least be comfortable there. A massive part that is easy to over look. Especially when you realise how hard it actually is.
Other than that. Stay on top. Control>punch>look for a sub or stay in the most dominant position you can. In saying that both my fights ended from in my guard. But I had a great sense of urgency on the bottom which is why I think I finished so quick after landing there.
see Gracie Combatives
nowaydo - see Gracie Combatives
Correct. If you already have solid Striking and wrestling then pretty much everything you need to use from BJJ in MMA is covered in Gracie combatitives syllabus.
vidavaletudo - One thing that is generally forgotten in pure bjj but crops up a lot in mma is keeping people down - bjj players often accept the bottom position to play guard while standing-centric mma fighters will pop right up from anything to a takedown to a loose side control transition.Was going to post this exactly and saw you already covered it. These days being on bottom is generally a death sentence, at least at the high levels of MMA. You will lose the round or worse. With that being said, everyone is trying to get back to their feet. In BJJ you get use to guys automatically defaulting to the guard. In MMA guys are fighting for their life to avoid the takedown or get back to their feet. You will be surprised when it gets slippery how hard it can be to hold someone down especially after a takedown or in a scramble.
Learning how to keep someone who didn't want to be down down as probably my biggest bjj -> mma adaption
Sweep the leg
I am a believer in rubber guard
Ttt for the good advices.
no tug o war
OP how's your cardio? and what weight are you looking at?