This is a highly subjective topic, but here's my 2 cents about how to "increase battery life".
1. The first is a matter of semantics. Do you mean "how can I maximize the serviceable life of my battery" or do you mean "how can I make the maximum utility out of a single charge"? To use an analogy, the first question would be akin to "how can I keep my car running for as many years as possible" while the second question is akin to "how can I get the most miles out of a single tank of gas".
2. If your question is #1, then the thing to do is to run on regular power as often as possible. All rechargeable batteries have a limit to the number of times that they can be effectively recharged (assuming you own a cellphone, you'll know what I mean, where a new battery can last for days but it's only a matter of time till that same battery can only hold a charge for about 30 minutes), and therefore the fewer times you need to recharge the battery, the longer it will last overall. Note that this doesn't mean that you should never run off battery power (otherwise what's the point of having a laptop?) but if regular power is readily available, I'd use it. Along these lines, when using battery power, it's a good idea to "exercise" the battery periodically by fully draining and fully recharging it.
3. Assuming your real question is how to get the most out of a single charge, you've already hit the main items: dim the screen brightness, do not waste power by running the CD/DVD, disconnect any devices you don't need (no point in leaving a thumb drive plugged in if you're not actually using it), etc. Personally, I don't use suspend in Linux
(if you're going to be away from the PC for that long, just turn it off) nor do I try to spin down the drives (wear and tear on the drive is not worth a few extra seconds of battery life)
That's just my 2 cents, I'm sure others have other comments -- J.W.