How to get strong quickly

A stronger team is more efficient
Clearing higher difficulty content gives much better rewards, especially in solo content, therefore your goal should be to get stronger as quickly as possible to clear Expert and Ultimate difficulties in Advent events.

Focus on one element for weapon grid upgrades
You have limited resources. Switching betweeen different-element teams to make use of elemental advantage can be effective early on, but you can use the same weapon grid for each team. Focusing your resources on one element will make late-game easier. See Advantages of a primary, dominant-element team for more on this.

R weapons and SR eidolons aren’t worth investing in
You’ll be getting rid of these quickly. Invest in off-element SR weapons or SSR eidolons instead. Don’t limit-break R weapons; save them for skill XP fodder.

LB0 Gatcha SSR eidolons are worse than event SSRs
They’re nice filler until you have a full grid of SSR eidolons, but don’t plan your team around them since their stats are severely capped. The sole exception is the +100% elemental attack eidolons. Plan your team around those and count on using them forever.

Farm events for a full grid of SSR eidolons
SSR eidolons from events will account for most of your team’s early growth. Element doesn’t matter much. Max level DOES. Farm as many copies as you can, up to 5. In general, prioritize SSR eidolons over SSR weapons, except when the SSR weapon matches your primary element AND isn’t Defender. Those will be situational cases that will depend on how useful the eidolon (mainly the passive buff) is.

Farm your team element’s Disaster to build your arsenal of Assault weapons
You can start 3 battles a day for each difficulty level, for a total of 6. Each battle can drop two platinum chests: one for spawning the boss, and one for MVP. SR weapons can drop from the platinum chests, and one of the three has Assault skill. There’s no difference in drop rate between difficulties, so prioritize Normal difficulty. Consider creating 2 alts to make use of BP, though the drop rate is much lower without the spawn chest. Make sure you get the MVP. During Advent events, focus your AP on event battles instead.

Level your weapons and eidolons equally
Weapons and eidolons gain stats linearly with level, but each subsequent level takes increasingly more XP. You shouldn’t be sacrificing weapons and eidolons for limit breaks until you have a full grid.

Focus your limit breaks on one copy
Your end goal is to have 10 max limit break weapons. Don’t do anything that will slow progress towards that.

Level weapon skills with an eye on endgame
Assault skill will take precedence over others. Level assault skill equally among weapons, but don’t level copies that will later be sacrificed for limit breaks. Raise SSR assault weapons to ½ the skill level of SRs. Don’t bother raising R weapons other than as skll XP fodder.