DW2 (tier IV) is the worst to grind
Scouts have primarily 3 roles:
1.Scout the enemy (preferably without dying). If you're passive you find a bush to hide in with good view range. If you're active you race around and try not to get hit. Optimally you wait until your team is ready to shoot at the enemies revealed.
2.Kill enemy scouts
3.Kill artillery, also wait until the enemy tanks have moved away from starting position and then make a run for possible artillery positions, revealing enemy positions on the way towards the artillery.
The tank destroyer lines play very differently. I'm on tier IX in British and tier 1-4 are fast glass canons, tier 5-9 are slow high armor/hit point with fast precision cannons, and tier 10 is a slow doom canon.
I've played mostly British, and their tanks fit well to my play style. What I find amazing is how different the tanks feel even though they're all just tanks.