This could be the first obstacle to be crossed, and it needs to be done well. Prepare for an interview by making notes in advance about the questions you want to ask and by being familiar with the family you're asking about. When the subject of your interview talks about Aunt Maude, you should know who she's talking about. Relatives may not respond well to you writing down notes while you are talking to them, so if you feel this is hindering your research then try interviewing them for information while recording on an unobtrusively placed tape recorder. Make them feel at ease so they forget they are being recorded.
Recorders make many people uneasy and they clam up.
Questions need to be specific. If they aren't then expect to fill up hours of audio tape full of rambling off-topic conversation. That interesting chat you had might not seem so interesting when you are listening to the tapes later. Specific locations, people and dates should jog a person's memory, to give you invaluable information. Once you have this base information write it down in a systematic way, and make sure you know the source of every bit of information, so any conflicting facts can be double checked and sorted out.