There's an incomplete guide, but as before the common ones are the hull MG mounts, viewports, the commander's cupola, and the turret ring (if visible). Those are pretty much universal, save for a few tanks that don't have one or two of them for whatever reason. If you're really dedicated, you can memorize the ones for popular tanks beyond the universal weakpoints.
The best description I've heard for what to shoot: "Anything that isn't a flat sheet of metal." "Anything that sticks out of the flat metal surface."
What I normally do? Since I driver higher vehicles like the KV-3 and T29, I prefer to aim for the hatch on the turret. A Type decides to hull down using my own hull? Shooting the hatch might kill a crew member or two and it's a guaranteed pen. Also, the hatch is generally large and easy to hit, even from 50m with KV-3.
Seriously, anything except a second sheet of armour is a weakspot (and that's mainly just the PzIV and SuperPersh). Bonus of weakspots is that many are located near a module or crew member, you won't just do damage, you'll cripple them, too.
As for how to start? It doesn't really matter, the first few hundred (thousand?) battles are the most important to learn basic survival and how you play. I'd suggest starting any line and going for heavies first. It's probably a nice idea to go for the KV first, the paper armour will force you to be tactical, while you'll get decent weaponry and even meet derp guns where you have to be patient and line up shots.
The KV-1 also keeps with that, except you get armour.
After that, you can go for TDs and SPGs, yet you still will know generic approach routes and how an average player fights and reacts (because either you will be an average player, or you'll be able to see how others do things)
There are many guides, but it's 500-1000 battles of experiences that will help you, no guide can teach you better than spontaneous destruction because you made the wrong decision. Trial and error, like DF (except that DF has guides that you can follow because there's less randomisation, your basic layout can stay the same.)
Speaking about DF: Go into battle chanting "Losing is Fun." (to yourself) and make it true; even if you do lose, try and make the most of it.
P.S.: Damn, I love making long posts that have no point!