Can I have suggestions what to do and what NOT to do when owning a new RP server?

There isnt much to say. Except, be patient, people will come. It takes time. Just dont be a noob about it. Or roll over and die.

dont use freeforums and use a proper domain and website!!!!!!!!!!!!!!!!!!!! freeforums suck

Buy vBulletin (not nullled), Get hosted tab, And host it. Also get a Domain for your vBulletin.
Have great admins, and don't have all admins and 1 player.

Make a new name (not SuperCool), don't host from your house, make a unique script (not GF)

vBulletin is soooo overrated, don't buy it. Stuck in the nineties.
Further: Use proper English. It's Tips for example, not Tip's (topic title).

That made me laugh (bold part). For example if I use phpbb forum, my server won't be popular? :D
Even with a free domain (.tk or w/e) it's possible to have a popular server.

And my advices:
First impression, really matters. When you start your server you need to work VERY hard for at least a week. When players see that you put a lot of effort to it (of course if that effort is making more fun on the server) they will come back. Maybe they'll bring their friends, their friends will bring their's friends and so on..
Of course a good advertisement (not only on sa-mp forums) is big deal.

I use it and i don't have problems with it ... Easy to use etc ..

What is your server's player count? 0?

We aren't blind, we can see without 4 thousands of "!".

Anyway, get your server in the hosted list, and it won't have 0 players most of the time.

As far as forums, go with PHPBB or make your own.