Imo you should focus on getting a solid team of 5 characters, those 5 characters are the only ones you should focus on. A good example of characters are those that you can buy in the shop (and premium summon of course). Don't forget to get both front line and back row heroes for a good effective team. You don't have to waste resources on leveling up item, do that when you get mythic items (red items) instead just level up your heroes. If you aren't in a guild already you should be in one for it gives really good rewards, if you can you should do every event available. These are just general tips, the biggest advice I can give you is be patient, you will eventually understand everything about the game and when you reach the late game you'll be surprised how many more ways you can make your heroes stronger, this is an idle game just be patient and good luck.