Resources
Make sure you complete the Daily Objectives as you will need a lot of resources and you can get a decent amount by doing them and they will help you progress through the game faster.
Equipment
It is important that you make sure that your team members have the best possible equipment at all times. This means that all six of the equipment slots are filled up, doing so will also increase their general stats and raise their Tier rating.
New Skills
Most of the characters when they reach Tier 3 or 4 will unlock new skills.
Challenges
Don't neglect the different challenges depending on the day of the week as these are a good source to get more resources on top of those you get from doing the Daily Objectives.
Collect Characters
Try to unlock as many characters as possible. Even though you only have limited slots on your team you will give yourself more options the more characters you unlock.
Upgrading
Make sure you prioritise your main characters when you level up. Leveling up characters requires a lot of resources so you need to focus on getting them to their max first before moving onto the backup characters.
Spending Cores
The only thing you should be spending cores on, is energy twice a day for 50 cores each. Literally every Orb in the game is a waste of cores.
Campaign Energy
Every Campaign battle costs at least 6 units of Energy to play and you will find that you quickly run out it. Energy recharges slowly over time but there is a special currency called Campaign Energy Refill and the option of spending Power Cores, the game's premium currency, to refill instantly.
Level 30
Most of the game's content is unlocked through levels. When you reach level 30 you will be able to unlock everything.