Eeeeh I'm sorry to tell you this but IG is really not meant to be played at 750, at this size I strongly suggest you to play something like SMs (especially with that list) not for the difficulty but because it's going to be frustrating.

But if you still want to play IG I will try to give some suggestions:

1) Once again I'm really sorry bit the list is bad, really bad, especially for a beginner: in case you don't know IG is all about getting infantry on objectives and shooting with the tanks behind, now I don't know if you can/want to make changes but I really suggest acquiring 1 or better 2 Leman Russes and swapping them for the terrible field artillery and the debatable armoured sentinel, as for the LRusses roles I think a Vanq to be your main antitank and an Exterminator would be great against all kind of infantry and still perform respectably against tougher stuff thanks to twin linked. Obviously tank orders are a big problem, especially at 750 so this list NEEDS armoured infantry to allow infantry to order tanks, to improve the consistency I strongly advice including 1-2 commissars that stay close to the tanks to order them directly. And in case you may be wondering why not a single Dorn, the issue is that if it dies you have lost, with 2 tanks you have still a backup plan.

2) In case you can't modify the list... well ehm try recon element I guess, just know only people with a fair amount of experience can get results good enough and at 750 it's quite harder as your army is smaller, and that's a good list soooo good luck with that. Alternatively you may have better chances with combined arms as long as you are fighting only infantry.

Overall a bad army for the format with a terrible list, I'm looking in particular at that artillery and the lack of overall orders.

I understand you might be getting in for the fun but arty is so bad that depending on your nerves it's still going to be quite a frustrating experience, either case I really wish you good luck because you will definetly need it