Don't wait, think it through, come up with a list of potential candidates, and promise yourself you're going to complete at least one family interview before this month is over. After all, October is Family History month!!
Your best candidates are those that are older than you and, ideally, among the most senior members of your extended family. Be mindful of health issues that may impact their ability to help, but if you can identify one or more senior members of your family that are in reasonably good health and with a clear memory, as well as an interest and ability to speak with you, then you're in good shape.
If you've not been in touch with someone in a while, it is best to announce your call with a card or letter. Let them know you're interested in your family tree and wondered if they might be able to help.
Prioritize what you'd like to know for each call. In some cases, finding out just one piece of information can well worth the time. Keep in mind what you hear is personal recollection and so it will need to be verified using other sources, but it's a great starting point. You may simply want to inquire about a maiden name or the names of brothers and sisters for a member of your common family.
If you can get permission, record the conversation (audio or video, in person or by phone). It will make it easier for you to listen without missing something. Even if you take careful notes, recording the call for later playback will be a great help.