@0v7:
I used Krita for a short amount of time - and by short I mean I just fiddled with it since one of my favourite artists uses it, but it drove me insane trying to use it with its backwards shortcuts and functions. I also tried the realistic watercolor brushes they added recently which I really liked but it didn't draw me in enough.
From what I can remember:

Right click color picks if you're using a brush or similar tool rather than bringing up the little tool panel
Alt brings up the color picker rather than ctrl
Transformation isn't it's own tool, it's just a function that has multiple modes. By default the scale/rotate transformation is ctrl+t
Ctrl+alt lets you drag out your brush size rather than holding down shift
Ctrl/shift+space lets you zoom in and out
Not entirely sure if Krita added normal clipping layers or are still only using groups, but you can activate clipping layers (they will only show what you paint on it in areas where the source layer is painted on) by clicking on the two ovals icon under the layer mode in the layers panel
Backspace erases everything on a layer rather than filling it with the current brush color, you can fill by pressing alt+delete or use the bucket icon in that top panel

A couple cool features I would recommend checking out:
- That top bar is called the command bar, and you can modify it by right clicking on it and going into the options. It lets you add different commands to a quick-access sort of thing so you don't have to search through a bunch of menus to find something you use a lot
- When you go into File > Preferences > Performance, in the undo section there's a feature called "undo intervals between actions", where you can change how long it would take between actions (brushstrokes, for example), so it will group together actions into a single undo so you can undo multiple actions at once and not have them all clog up your undo history

My tips are just try to fiddle around with things, mess around with how things are arranged, edit your keyboard shortcuts to whatever you'd like, download whatever you need from the Assets gallery (you can find that in the materials panel, it's very handy and automatically downloads and installs all the brushes/image materials/3d models/color sets/etc into your materials panel). I know maybe too much about the program so just ask and I'll probably know what you need, if not there's a whole forum for issues with the program

Edit: Also!!! I hand copied over more accurate gradients from the original Voltra photoshop gradients, since when the pixel guide first came out the there were no gradients for other programs. The psd file Vozzy provided, for some reason not all the info carries over correctly so they're kinda simplified and not accurate. I can make a quick guide on how to save all of them if you want, it's a bit tedious but worth it in the end, I can also make a download for my own gradients, which is in a .clip file rather than .psd.