What Rex_Nex said (especially in regard to why Sixth Sense needs to be changed around, heh). It depends on a massive number of variables--your tank, your team's tanks, the enemy tanks, the map, the map-wide tactical situation, the localized tactical situation, &c., and there is little to no forgiveness; if you fuck up you're almost certainly going to die. But basically the one thing you should never do is point towards the enemy base and open the throttle.
Generally though it'll break down into four main roles:
1. Passive scouting, aka bushscouting. This is where you sit, hide, and use your camo to light up targets for friendly tanks and arty.
2. Active scouting. This is where you drive around keeping tabs on the enemy team. You should generally try to avoid staying in line-of-sight to any given enemy for more than a second or two; the key is to pop in, light them, and move on before being shot. This also encompasses lighting targets by driving right up to their cover to abuse the minimum spotting range.
3. Arty-killing. If the other team gives you a gap in their lines that you think you can make it through, gun the engine and try to pick off their arty.
4. Harassing. This is for tanks like the French scouts, the Chaffee, the T-50-2's replacement, &c. that have guns good enough to penetrate mediums/TDs/maybe even some heavies from the right angles. Basically it's like active scouting, except you're looking for chances to flank enemy tanks and put shots into them. The goal here is to either do free damage to more important enemies or to draw their attention away from your own team. This can be accomplished either by sniping or getting in close and circling a lone enemy tank. The T-50-2 in particular was notorious because it was fast enough that only a bare handful of tanks it could be matched against could traverse their turrets quickly enough to catch one that was circling them, while also having a good enough gun to penetrate a lot of high-tier stuff from the rear/sides/weak spots.
But more than anything else, you have to have really good awareness both of what's going on around the map, and of your local situation, in order to be able to position yourself correctly. A lot of it (especially knowing when is right to charge in &c.) is a matter of practice.
Aside from that, always buy your engines first, radios second, and everything else after that.