David 'crt' Wright, author of the Keygrip2 program, sent this post to the Quake2 Demos mailing list last year.  I thought about re-writing it for this site, but I really can't say it any better than he did.  These tips have proved extremely valuable to me, and I hope they will be for you as well.

From: "David Wright"
To: "Quake2 Demos And Movies"
Subject: [q2demos] Movie tips (was skins)
Date: Thu, 6 Aug 1998 15:28:08 -0700

While I would agree that it is VERY important to film it "right" the first time, I think you underestimate the value of recamming, especially considering the total lack of good Q2 camera patches.

FYI, I recommend the following when making a movie (not everyone can meet all these requirements.. but you should try for as many as possible)

• Use a dedicated server on a LAN or fast net connection
• Have your main "cameraman" on a cable or T1 connection
• Record client demos from every actor (not just the cameraman) as well as a serverrecord demo, even if you just plan on using the cameraman's demo
• Record client demos with cl_nodelta 1 (unless you are on a slow net connection). This will help alleviate some of the block size problems.
• Make sure everyone joins the server in the same order each time you film, otherwise you cannot (easily) cut/paste between seperate demos
• Record lots of short demos with identifiable names, instead of one HUGE demo of your entire session.
• Once you are done filming zip a backup of your demos directory so you don't risk deleting or editing an original by accident
• Agree on the script beforehand and make sure all your actors have read and understand it. Trying to give directions and positions on the server while filming is often difficult.
• Get experienced and appropriate people to do the voice acting. If you need a person with a deep voice then find someone! Don't try to fake it with filters in your sound editing program.

If you have to do this voice acting yourself, follow these tips:

• Use a HIGH quality microphone. The one bundled with your SB16 won't cut it.
• Control your breathing and don't hold the microphone too close. Breathe through your nose.
• Shut out all ambient noise and record in as quiet a room as possible. I recommend moving as far away from your computer as your cord will allow, since computers often add a lot of noise.
• Never try to play music in the background while you are talking - mix it in later.
• Record at high quality, resample to lower quality - 8khz, 8 bit, mono is usually fine for voice. [Ed.- I prefer 11.025kHz]
• Programs such as CoolEdit [or Goldwave] have noise filters. If you recorded your source material correctly these SHOULD NOT BE NEEDED, but may help after the sound is resampled. 
• Get someone to objectively listen to and evaluate your voice acting abilities before you release anything.. you hear your own voice very differently from how other people hear you.
• Unless you are very good a improv (/me looks at Clan Ill) write and memorize your script. Do not try to read while recording! It is very obvious. Memorize and practice your lines like a real actor!
• Finally: DONT OVERACT! Be natural.. don't change voice volume or pitch too quickly, stay in character, and don't switch characters without a break.