Hi Jörg,

> I need to watch more tutorials to understand how to model in Moi working properly
> in order to get a clean result.
> Do you know a tutorial that such topics treated?

I don't really have a whole lot of tutorials in general - the ones that are available are listed here:
http://moi3d.com/resources#Tutorials

One general tip is to try and build some pieces more as extended pieces initially that then get cut to their final outline, rather than going around and doing things in a "patch by patch" manner.

There are some tips for people from a poly modeling background here which may be helpful:
http://moi3d.com/forum/index.php?webtag=MOI&msg=4865.2

- Michael