Some humble advice from years of experience...
1. Be persistent - follow up on every lead, don't assume records aren't available until you've done an exhaustive search
2. Be thorough - analyze every detail of relevant records, and be liberal about what you consider a relevant record; expand beyond your immediate family and look at the development of the community as a whole; contact archives to find obscure record collections
3. Build and maintain relationships - success in genealogy depends a lot on shared information
4. Don't let language be a barrier - you don't need to be fluent in foreign languages to research foreign records, you can often get by just fine by identifying key names and places and using online translation tools
5. Don't let overseas be a barrier - in today's age, it's easy to communicate with foreign archives and genealogists by email, payments can be sent with relatively inexpensive transaction fees, and more and more records are available through online databases accessible anywhere
6. Acquire records now and preserve them yourself - don't assume that records will always be available, many records and cemeteries have been destroyed relatively recently by wars, fires, vandalism, etc., record accessibility laws can change, archivists can become less cooperative, relatives die, memories fade...
7. Be skeptical - hardly anything in genealogy is absolute and is only as 'true' as the evidence it's based on; use information from other researchers, but don't accept it blindly; consult original sources, whenever possible, to reach your own conclusions; the desire to fill in names and dates in a family tree can often lead to accepting things without good evidence - theorizing is important and useful, but should be qualified