It would be more helpful if you could describe why exactly you're having problems driving Manual. Are you not used to having to shift for yourself, are the buttons you're using too inconvenient, or are you using a wheel? Or is the car tricky to drive Manual?
Either way, I can list some generic ways to help you. If you're using the DualShock 3 (DS3) controller, I'd suggest you change the shifting buttons to either the L1 and R1 buttons (I personally use this setup), or the Face Buttons if you're using the L2 and R2 triggers to brake and accelerate. There's less travelling distance in fully depressing the L1 and R1 buttons as compared to the L2 and R2 triggers, so you can shift with more precision in timing. Not to mention, changing to the 1 buttons have solved my "argh, you stupid game, I so shifted, why didn't you register it?!" problem. Although, since I don't use a wheel, I can't offer any advice on them, sorry.
I would also advise you start with a car that has a very even torque curve. Even as someone whom has been driving Manual since GT2, cars like the Suzuki Escudo is a nightmare to drive on Manual given it's atrocious torque curve. You'll want something that willingly accelerates at pretty much any RPM, just to get the hang of it. I'm not a big fan of the car, but I'd suggest the R35 GT-R. It has a very useful torque curve, and it's gear shifts are fast, both traits helpful for learning to drive Manual in the game. Of course, the R35 wouldn't be good for drifting whatsoever. You might want to consider any of the numerous FD RX-7s in the game for that. It shifts really fast for a stick shifter, and it's torque curve is really generous with it's twin sequential turbochargers. Of course, this is coming from a RX-7 fanboy, so take it with a grain of salt
Either way, you'll probably want a loud car. Something like the Viper ACR just won't cut it. You'll want a loud car because you want to keep your eyes on the road as much as possible, which means you wouldn't want to keep your eyes glued on the tachometer. Heck, the tachometer is pretty much invisible, even in most Premiums, unless you're racing at night. Once you find a loud car, you can try accelerating from a standstill from 2nd gear or 3rd gear, to learn how the engine sounds like as it revs from idle to redline. Learn to listen for when the Engine is about to hit the redline- it's distinctive sound at it's distinctive RPM. This is something that cannot be learned through text alone: you'll have to practice it for yourself. It's going to be infuriating to over rev the engine and have the revs bounce back, but use that frustration as a warning next time the engine is about to over rev and shift up.
Also, one last tip would be to take corners in one gear. Shifting gears mid corner is a really awkward thing to do, since you'd be cutting off your gas and shifting the weight of the car to the front mid corner, which could upset the balance of the car. However, this is exactly the advantage that Manual cars have over the Automatics in the game, in addition to Manuals generally being lighter in mass than their Automatic counterparts in real life.
