What advice/resources can you suggest for new communities? Are there any guidelines or tips? Does Lego provide any resources on this matter (other than sets for contests & co)?
First check and see if there is a LEGO Users Group in your area: http://www.lugnet.com/map/
You may need to start a new LUG if other groups are too far away. Check out websites of current lugs above to see how they handle meetings and events. You will need a meeting place and a website to promote your club.
TLG has supported lugs in the past by donating small amounts of brick for displays and catalogs, posters, etc to give to the public at events.
Online communities are formed by like minded fans without the support of TLG. Find other fans at existing community sites. Discover the people that are interested in starting a new site. Check out the major theme and community sites to see how they organize their forum, set archives, article sections, events, etc.
From time to time TLG donates new sets for contests on major theme sites such as Classic-Castle, FBTB.net, etc. Thanks TLG!
In the past certain Lego resource sites have been assisted financially by TLG until they became self sufficient. Currently it is unlikely that a new fan site would have this level of support.