Negate using Ghost as much as you can. That playstyle will be pretty useless in this game. Try running Flak on alot of classes with SoH, Tac Mask. If you havent already.  Lightweight is out, so use Scavenger. Its a must to use MP5 because its coming back. AK47, though that gun is not for every map. You still have time to pick up MW/MW2 if you choose to. They are reasonably cheap and they would complete the series as of now anyway. They are totally different games compared to B Ops. Try it out and see what you think about the feel. Hope I help.

Sadly I would save your money on Cod4/MW2 for now. Both games are hacked like crazy. For what its worth cod4 is still the best game IMO and hopefully mw3 is similar.

I would also try and stop dolphin diving too as this is not in MW3,

You are right in saying BO and MW2 play completely differently.

As esmorgue has suggested I would try and pick up a used copy of MW2 or rent it a week or so before MW3 comes out.

In my opinion MW2 plays alot quicker than BO, When I went back to MW2 after playing BO for 8 months I was surprised how slow I had become, and I used to do quite well in both games.

If you dont want to/cant get on MW2 try thinking and acting faster, and aiming faster in BO.

Scavenger is always a good perk to run, i would also try sticking to guns with higher recoil, such as the AK-47 as the recoil has become more apparent in MW3.

I am currently playing MW2 in prep for MW3 and trying to use the SCAR alot as this has a good amount of recoil.

Hope this helps.

By playing MW2.

Don't even bother with MW2 at this point; There are only 17 days left for MW3. (18 days from your posting date)

It's not difficult going back and forth between MW2 and Black Ops. As long as you get all the info on guns, perks and poinstreak packages, you'll be able to hit the ground running when MW3 hits. (assuming MW3 mechanics are like MW2's mechanics)