Hey Petr,
1. The links from a site on the same server won't do much for you.
2. If you want to get a back link from another site, it would be better to write something original for them and do this for many related sites.
The last two practices don't really work any more.
You should try to combine social with video and embedding. Get social buttons on your site. Make a Facebook page, slowly share your pages on digg, delicious, twitter, reddit, and StumbleUpon.
Shoot some quick videos using screen capture (CamStudio is free) and OpenOffice presentations. I can't read your language, but it looks like mortgages? Quick 1 minute videos about tips and basics is always very easy and effective.
Embed those vids in a relevant post.
You really need to be stand out from your competitors and search is losing its market share. Target the traffic across multiple types of media and social sites and expand your horizons!
SEO is an ongoing, constant process that you need to constantly work at. You'll get there.
Best of luck!
Jared