Divinity: Original Sin 2 is a huge game that, despite of having a rather complex tutorial (Prolog), throws players in at the deep end without giving enough explanation for many game mechanics. In this chapter, you can find a few advices that can be helpful from the beginning of the game.
1. Pay attention to characters' backpack capacity. You must regularly get rid of unwanted items so you won't find yourself in a situation where all your characters are overburdened. In the later part of the game, when you get access to Lady Vengeance ship, you will be able to send items to a chest located on its deck - you simply have to click on an item with right mouse button and select "Store on Lady Vengeance" option.
2. Click on everything and everyone. You never know if a person can give you a quest or give you interesting information regarding the game world. If a character doesn't want to speak with the main hero you should start a conversation again by using another character from your team - thanks to that a conversation can go differently.
3. Check all containers. Chests are the most tempting ones because they often contain valuable items, however, barrels, wardrobes or potion containers are also worth checking out because they can give you a lot of valuable items and/or gold. All caches should be opened with a character that has Lucky Charm skill - the higher the level of that skill, the bigger chance for finding a magical item or more gold inside of a container. Thanks o that you can even find a legendary item in any of the caches!
4. Speak with animals. This can be done only by a character that has Pet Pal talent (you can't speak with animals in any other way). However, you can get this skill only thanks to two companions - Ifan-Ben Mezd and Fane. Conversations with animals allow you to get additional information about the game world or make progress in a quest (e.g. "Lady o' War" main quest). Keep extra attention to animals that have a unique name (instead of simple "Rat" or "Dog").
5. After a few dozen minutes into the game the team will be accompanied by a Black Cat. You can't do much with it besides a short conversation (thanks to Pet Pal talent). However, after escape from Fort Joy's prison you will be able to use additional services of that cat. You should protect it because you will be rewarded. More information can be found in the chapter: How to save the Black Cat?
6. You must save game regularly. There is nothing worse than spending a lot of time on configuring characters or on trading and having the game crash or making a mistake that leads to death of your entire team - and all of that without making any saves which forces you to do everything again. Use both regular saves as well as quick save and load options (F5 and F8 keys). You must also remember that the game can be even saved during a conversation with an NPC - if your choice isn't what you wanted you can simply load a save and try again! Number of automatic and quick saves can be increased in options (Options -> Gameplay) - you should move both sliders to the maximum number which is 25 save slots.
7. Keep an eye on shape of terrain as well as additional objects and use them to your advantage. A hill is a perfect spot for an archer - they can deal additional damage and have a better range. A barrel with poison or oil can be set on fire - you can deal a lot of damage at a low cost. However, you must remember that enemies can also use terrain and its advantage.
8. Find a shovel and a bedroll as fast as you can. A shovel allows you to dig up hidden treasures or reveal secret passages that can lead you to additional quests and/or characters. A bedroll can be activated and thanks to it the entire team can get back all their health points and both types of armor as well as remove all negative statuses (besides the permanent ones). In addition to that all characters get a buff that gives them +1 to Strength, Constitution and Intelligence. Shovels and bedrolls can be bought from many merchants. However, you can find them right in the beginning of the game - more information can be found in "Where to find a shovel and a bedroll?" chapter.
9. Remember to highlight items by pressing "ALT". This shows you all information about items lying on ground that can pick up. You must also remember that you are not allowed to pick up items that are in red - when you pick them up you simply steal them so do that only when no one is watching. Another important information is that "ALT" doesn't highlight containers and chests - only items that you can pick up.
10. Field of view of your characters and enemies can be checked by pressing "SHIFT". When you do that you can see red areas on the screen - they indicate where a given character can see your heroes. There are two types of areas - when a character sneaks in the darker one they can remain undetected but when they are in the brighter one then they will be detected immediately.