Choose a quiet environment for your focus group discussion.
You may want to use external microphone(s) in order to pick up all voices clearly.
Turn off mobile phones where possible. When a mobile phone searches for network coverage it interferes with recording equipment and can obscure voices. This can happen even if mobile phones are switched to silent or vibrate modes.
If identification of the participants in the focus group is required in the transcript ask the participants to introduce themselves and say a little about themselves initially for identification purposes.
Remember, your transcription services provider has most likely never met the participants in the focus group so identifying voices is extremely difficult. The facilitator of the focus group can help by saying the participant's name each time a new participant speaks.
Wherever possible supply the transcription services provider with a list of participants and any technical terms referred to throughout the meeting.