I wallpapered a wall for the first time last year, full of trepidation and convinced it would fall off. It was easy, quick and so so so much less annoying and more effective than painting. Now I'm working my way through the whole house.
Get 'paste the wall' paper, it's nice and thick so covers a multitude of sins, it's also really easy to hang, you don't have to do any of that paste, wait for it to soak in, fold it into a weird configuration then finagle it to the wall stuff.
Use a plumb line to draw a straight line where you want your first bit of paper to go.
Slap ready made paste onto the wall using the biggest brush you can find, be generous and really spread it out.
With the paper still on the roll, start at the top and roll it down the wall.
Use a wallpaper smoothing tool to press the paper flat against the wall and then to form a nice sharp crease at the bottom. Use a Stanley knife against the edge of the smoothing tool to cut along the bottom.
Get a damp cloth and sweep it all over the paper from middle to edges to smooths out any paste bubbles.
Then repeat with the next piece until you've done your whole wall.
If you need to you can gently move the paper around a bit to get a nice close match between each length and to match any patterns.
Give it all another wipe over with a clean damp cloth to get rid of any rogue bits of paste then trim up the top line if you need to.