If you've seen video sales letters in action, you'll notice 90% of them are ... just bad. The worst ones are the straight powerpoints with some dude reading the slides. (Caveat: Sometimes even they convert like crazy depending on the audience).
1. You need to have good copy even with VSLs, and there are many formulae including AIDA that can be applied to them. You do need to hook them in the beginning and sometimes just whiz-bang graphics does it. (It's really simple especially with guys because we go .... "Oooh shiny").
These are not expensive and you should be able to get stock video for 30-50 bucks (For 100 bucks the talented guy/gal who wrote it will even customize it for you).
2. Get your script done before you record. Read it and refine it till it sounds naturally "you". Read it with lots of excitement and emotion. It's a performance. Get audio talent if you need to. Lot's of talented people are available on the cheap.
3. Clean the audio. This is an important and often missed step. It's easy to do with programs like audacity. At the bare minimum, remove all background noise. You can be quiet for 10-20 seconds before you record to get the "background noise" signature for removal.
4. Add music to your audio. Lots of stock audio is available both paid and free. You can use software like Garage Band (or a PC equivalent) to do this. The music can add emotions but should not overpower the audio. (Pay attention to the background music in movies).
5. If you're using PowerPoint or Keynote, keep less words on the screen and add some imagery. There may be a difference of opinion here but people don't like being read to and tune out quite quickly. (Even when you're doing a live presentation NEVER read your slides). Each slide represents an idea that you are explaining.
6. Add enough movement to keep people engaged. Something should move around every 30 seconds or so whether it's text landing or an image moving or other stuff going on. Movement attracts attention.
7. Once you've got all these pieces then record. Run the music and start clicking through the slides, transitions or anything else you have.
8. (Optional) When you're done use the audio in the recording to match up to the separate audio you have and move it a few seconds early so things land on the screen as you're speaking. Check if it sounds and feels natural.
If you do follow all these steps, you'll be proud of what you've created and get compliments for your video (and more importantly get more sales).
Oh btw, someone *is* going to come back with a bloody retort about a real example that I've done so ... here it is (It's not in the "usual" market and it's not a sales video ... on purpose).