Since I have a friend that has been playing for about two weeks, and recently started a side account so I could check out the state of the low level game, I have quite a few things I can pass along here:
Join an active guild or at least one you can keep pace with.
Buy one of every weekly glory troop from the shop. This is possible just from the glory rewards from the first three red guild tasks (35k total for the entire guild) and either tier 1 in PvP or with treasure maps to fill in the remainder. If you have a faster guild, you should also have this just from opening the 670 glory keys plus the 360 glory you get from the red task.
Depending on how fast you progress, the middle and left PvP option may be easier than quests.
Difficulty (and its bonuses) do not apply to ranked PvP.
Don't be afraid of PvP. You don't need much to be effective super early in the game. Always play Ranked PvP, whether or not you are interested in the ranked rewards. Losing points won't cost you anything, and gaining them gives the possibility of tier rewards. "Casual" PvP is pretty much entirely useless.
Level all kingdoms to 5 as soon as possible for early tribute chances. Collect income as often as possible for more tribute chances.
Level magic kingdoms to 10 first, then the stat of your preference.
Other things being equal stat wise, prioritize Glory tribute for leveling kingdoms.
Do challenges when you need the souls. Wear your best soul bonus armor and play on the highest difficulty you can take to maximize the one-time reward. Don't be afraid to complete them if you need extra souls early on - the total available from challenges is not that much overall, and should be used as a small bump to bridge a needed gap before you can effectively farm.
When leveling troops to get kingdom points for star levels, only commit resources when you know you have enough to reach the star. Level troops one at a time to conserve souls, as every level gives the same points, but higher levels cost more souls.
Wight and Banshee are now effective early game soul generators. Very early on, they are better than Valkyrie.
Don't bother saving treasure maps, they are easy enough to get later on and you probably wont want to play treasure hunt later anyways.