For telephone interviews use a telephone recording device with the capability to record both sides of the conversation. Avoid using speakerphones if possible.
Use an external microphone.
Set your recorder to the fastest speed.
Turn off your recorder's voice activation feature.
Use fresh batteries - make sure the battery icon shows full power for each interview.
For multiple speakers, meetings and focus groups, use a conference recorder with multiple microphone capability.
Record in a quiet environment (preferably behind closed doors).
Place the microphone(s) as close to the speaker(s) as possible.