Do not play this game like you would play Skyrim.
Geralt:
In the Witcher series, of which I tell everyone to pick them all up, you need to use EVERY ability you have.
Take the time to sort out alchemy, it will help you in every quest. Literally every quest.
I said every quest right? because it helps that often......
Do NOT rush through the game, you will miss out on a ton of really quick and easy side quests that give gobs of XP. The game will assume you did them when you get to a new area, and NPC's will be of a much higher level than you. (Seriously, some quests are as simple as fixing a broken altar. Just move this stone block and BAM done, 2000 XP)
Loot the shit out of the battlefield near the starting town, wander up and down it a few times, take all the crap to the dwarf, and salvage it.
When underwater, you can only use the crossbow.
Oh yea, and Alchemy is your friend.....
Ciri:
You don't have to be as patient with Ciri as you do with Geralt. Her portions of the game are there to provide backstory and update you (Geralt), about what is happening in the Novels.
You can run through quests as her, and it will be fine. (Or at least I never noticed a penalty.)
Also are you on PC or PS4?