World of Tanks on Playstation 4

Most SPGs have rather small gun arc so you need to plan what you do beforehand. Most SPGs with big gun arcs are the ones which were added in 8.6 patch (the patch that nerfed SPGs to the ground). That means you need to know the maps well, know where you can shoot to which positions and where the enemy is going to be usually. Plan ahead and preaim, dont be hasty in swapping targets around the map and focus on one area at the time. Patience is needed and its quite dull at some points too, unfortunately.

Buying gold ammo for SPGs is not really needed. I have 2 T10 artys (US and French) and I havent really used any premium ammo along the way.

You could play in a Junior Tank Company. Additionally, leaving Assault/Encounter mode checked when playing low tiers allows you to get into those matches with your low tier tank. Since you need to have unlocked a Tier 4 and Tier 6 tank to play those game modes respectively, most players in those game modes will have more experience on average than you'd get out of a normal battle.