one problem I realised was, that students usually do not look into Moodle regularly. Thus is would be nice to be able to inform them about a new or changed item. How could I do this best ?
Thanks for your help!
You could set the news forum to force everyone to be subscribed and then make posts encouraging them to checkout the new items. This will send emails to all students enrolled in the course with each news post you make. You could do the same thing with a totally different forum and call it something like "what's new?".
As Marc indicated, you might also build something into the course to help change behavior so they are actively in the course without your prompting.
One way to do this is to offer points or bonus points for the first person to identify that new material was posted. You could create a forum for them to post their finds. This will help students know it's really happening and help create some healthy competition!
Another way may be to hide some "easter eggs" in the new material and have students post the "easter egg" in a forum.
Hope this helps!
As Scott mentions, posting to forum with mandatory subscribe or requiring some kind of rss practice will get the "news" out, but planting Easter eggs (this has a bit of a special meaning in IT) or implementing the same thing via a scavenger hunt will teach your students academic discipline that will have many future returns. There is a great deal published regarding effective reinforcement schemes, but let me know if you need further assistance in that regard.