How to improve my animation skills and portfolio for game dev?

That question belongs in the Visual Arts forum. That's where the artists
and animators hang out and discuss.

Where can I find a job?

Where do you live?

Ukraine. Right now I'm looking for a freelance job.

Freelance isn't a job. It's a way of life, and you need to find gigs (not "jobs").
For freelance, you need to have a really good online portfolio (with a body of
finished games you've contributed to), and a list of contacts (people with whom
you've worked on games, and who trust you), and you need to network like crazy.
Go to game developer meetings, conferences, trade shows, etc. I recommend you
start by subscribing to GamesIndustry.biz and Gamasutra.com
Good luck!

[edit] Also check out gamedevmap and gameindustrymap (both are .coms)