Overclocking's just fine so as long as you don't push voltages too far as nc50lc said. Some softwares like Blissz's firmware for the L3+s automatically calibrate to the lowest stable voltage for an overclock, and you can also manually calibrate voltages on software that doesn't do this for best performance. As long as you're running the miner in normal conditions and keeping up with maintenance like occasionally clearing out dust for optimal thermal performance as needed, nothing bad should happen.
Where can I find more info about periodical maintenance? That was interesting and Blissz software was also interesting.
Bitmain provides a pretty basic guide about what sort of maintenance you should occasionally do on a miner in a subcategory on this page (click here for main page link, and here for Bitmain's provided maintenance page). To summarize what Bitmain says, they suggest to dust out the miners monthly, though I do this per two or three months. Helps to keep temps under control since dust can do a lot to raise temps. The guide shows a person using an air compressor to clean out the miner, but canned/compressed air for computers is good too and what I personally use. If the dust is heavy, you can always disassemble the machine and manually clean out the heatsinks for dust.
]