Leaving card(s) unnatended, mining 24/7 at a stress and power usage perhaps equivalent to Furmark(?) is a different purpose and scenario for using this device. Very different. Here you want to optimize your hash rate, for profit. Having low hashrate, using too much power, killing your card or even setting the house on fire is surely detrimental to your purpose.
Now to the point... How to OPTIMIZE your videocard for hash speed, low power and safety.
If you have a 7870XT, 7950, 7970 or 280x videocard, go and post on this thread: https://litecointalk.org/index.php?topic=12369.0 Donate/pay upfront for the service (if you have a card, you already mined coins) and post your ORIGINAL bios. Wait patiently and grab your modded bios.
For serie 7 videocards, R9-270 and R9-280 you should lower the voltage of the bios to 1075 mV or below with: http://www.techpowerup.com/forums/threads/vbe7-vbios-editor-for-radeon-hd-7000-series-cards.189089/. Visit this thread for some comments on bios flashing and hash speed/low power usage tips and optimization: https://bitcointalksearch.org/topic/m.4500529
Running on default voltage will KILL or seriously reduce the lifespan your card, so you MUST lower the voltage. Mining 24/7 can destroy the voltage controller, capacitors or the rest of the power block, even more if they are cheap sourced and don't have proper cooling. Some people had their cards throw sparks, put out smoke and even catch fire.
You must make sure you have information about "VRM temperature" on your card. See screenshot below. If not, you're mining "blind", praying, and in this case you MUST lower the voltage even more.
You also MUST run the fan at decent speed, at least ~70%, even if sgminer shows low core temperature, to cool the rams and power block. Note that the GDDR5 rams are hammered at scrypt mining with unusual access patterns, considering that cards are game accelerating devices. rams tipically have no cooling, no heatsinks. The effect of scrypt mining on rams is unknown for me atm, but artifacts are to be expected if you want to play games later or sell the card to a gamer, despite error correction. Don't push the card fans too much though, because they can degrade quickly too at max rotation. You should provide extra cooling for your cards, pointing an household large fan to your rig.
Then go to the link mentioned above, pick sgminer and those .bin files on the top comment: http://www.reddit.com/r/litecoinmining/comments/1va8g2/ann_sgminer_400_release/
Copy those bins to the sgminer folder and either use on your config:
"thread-concurrency" : "24000",
"gpu-threads" : "1",
"intensity": "20"
or
"thread-concurrency" : "8192",
"gpu-threads" : "2",
"intensity": "13"
Use also:
"gpu-memclock" : "1500",
or
"gpu-memclock" : "1600", if it's stable and faster.
For "gpu-engine", start at ~950 and raise it 10 Mhz at a time until you max out the hash rate and while the card is stable, of course. Somewhere from 1000 to 1100.
GPU0 is my cheap brand 7970 card pulling now 790 Kh/s at the edge of stability, for a screenshot. It's usually at 770 Kh/s and for shits I already pushed it to ~820 Khs but I was not happy about the required voltage and power consumption. Before, I was at ~680 Kh/s with 710 very hard to reach.
Note the acceptable values of "GPU temperature", "VDDC", "VDDC current In" and "VRM temperature". If your card VRM does not report those values, you have a subpar card for mining. Undervolt more and be content with decent speed at low power usage.
Feel free to correct and add further tips. Note also that this is about videocards only. Nothing here discusses the remaining good practices, the REQUIRED high quality PCI-e risers, motherboards and GOOD Power Supply Units