Here is what I focus on:
1. I use good, stable UPS's, make sure the batteries are always running properly.
2. I use fast networking gear (switches, NICS in the servers, wiring, etc)
3. I buy low cost desktop boxes that support 32gb or 64gb of RAM and I am considering stepping that up to more as a max potential.
4. I max out the RAM in the boxes from the start. Saves needing to power down, install time, power up time, etc. May not sound like much but it is some savings.
5. I keep backups on a Drobo (16tb) for each server. In case of a failure I am able to restore fast after installing a new drive.
6. I run a pfSense box front-ending everything
7. I am on Comcast business a lot to provide the best service, stay competitive in price and make sure I am always running their latest modem offering.
8. I have daily logs e-mailed and I review quickly for anything major and then a weekly appointment with my servers to check them more in depth, run updates, etc. We only run CentOS.
I'd be happy to talk more about how I keep this in check or provide any more details.