Attack early and often
When in combat, it's a good idea to think more offensively in certain situations. Remember, it's turn-based combat so you'll have to think about what your next move is going to be. Attacking consistently is good simply due to the fact that you'll be bringing enemies' health down faster.
You start off with two characters and need to manage both of their health bars. You can get either one of them to attack in combat. You will get hit eventually which means some of your health will be gone. However, you can replenish it if you have items in your inventory. You can then choose which character you want to heal.
Having healing successfully, continue to pile on the attacks. Go for the kill. Finish them off as soon as possible. Unless you know your foe can deal incredible damage, then there's nothing wrong with being a bit aggressive if the window of opportunity is there to do so.
Make sure you have ale on you
Since we talked about the importance of attacking early and often, it's also highly critical that you make sure you have some ale on you. There are different kinds of ales, and each one will replenish your health. Have some handy one you at all times if possible.
If not, then just unleash as many attacks as you can to take down your enemies. The good thing is that usually, one ale (especially the green one) can recharge a huge chunk of your health. When you go up against bosses, they usually tend to have special abilities that deal great damage. Having this ale on you is a life saver.
There will be other items you'll gather on your journey too that will make things easier for you. Just make sure to come as stocked up as you can before heading into battle. Just because it's good to attack often, doesn't there's never time for healing up.
Take in the environment
In a world as interesting as The Greater Good's, you'll have plenty of chances to just soak in everything. And not just taking the fascinating locations, but doing other things as well. Try interaction with as many things and people as possible (especially save points because you can only save manually).
You never know what you'll discover. And when talking to different folks, it's always fun to read the dialogue bubbles. Some conversations will be important, while others won't matter at all. It's just always interesting to see what others have to say about you, the current situation, and everything else.
You can't have a good RPG without the ability to interact with stuff, so definitely make sure you take advantage of your surroundings. The more you can absorb, then the better. Interactions help bring an extra layer into an already pretty deep game.