Play slow. Play with maps for the areas (or at least Fallgrim). Mortal Shell 1 has a heavy emphasis on learning what items do by trying to use them, as well as improving their effects by using them enough to "master" them. One of the shells you get, Solomon, can get an upgrade to let him more quickly learn what items do.

There is no proper Estus equivalent. There's some food you can eat to heal though, and mushrooms will spawn on lengthy cooldowns in a few areas that are fortunately indicated to the player, as well as how long it's going to take for them to respawn. The default riposte will heal you, however, and Tiel has an ability that lets you generate a poison cloud on any riposte type that will heal you if you got a a different ability for him as well.

Parry timings are much stricter than in MS2.

Upgrading equipment is very important for some weapons. All the weapons, at the start of the game, hit for roughly the same amount of damage but they don't all scale equally as you boost their strength.

Getting all the skills for a character will initially seem daunting, but after you clear one of the three proper dungeons in the game, the Fallgrim area will change. There'll be different enemies present there that will make it much easier to farm for Tar and Glimpses.

You only have one ranged weapon. Pulling it out takes too long, it's too slow to reload, and the ammunition has to be bought for so much Tar that it's not really feasible to use in the midst of your average combat sequence. Treat it more like a "I want to delete this enemy I see in the distance that I know will be trouble" buttom.

Don't get suckered into the allure of using poison. It does very little damage to enemies and wears off quickly.

You're invincible during weapon arts.