I've done my own, I went on a weeks course a few years back and I've since then have effectively plastered about 2 houses worth over the time. I take my time and tackle only the amount I can do comfortably. I'm also still very messy.
It's definitely a skill to do, as said above it's not something you can pick up quickly, definitely not from the internet...you can only get good at it by doing it, and doing it a lot....pros make it look a doddle but it's not at all.
Lots of facets to it, getiting the mix right, getting it put on in time without it going off being the biggest to overcome.
If you're interested in doing it in the future I'd say give it a try...if it's only skim you could probably just pay pro to do it after if you're not happy (and you've not made it too uneven, or have to chip it off). Otherwise if it's just one room, just pay someone, if you're picky like me you won't get a good enough finish if you've never tried it before.