1. Never ever mine Bitcoins at a loss. If your mining can't even recover the electricity costs, then stop the mining. Sell your mining equipment, and buy a few coins from the market using fiat.
2. In case you are mining at a profit, then sell 80% of the coins to cover your expenses, and keep the remaining with you.
These are quite normative recommendations. I think a lot of miners continue to use their equipment even when it is not profitable anymore, because they speculate Bitcoin valuation might be higher in future. Also if your equipment is not profitable anymore, you're unlikely to get much if you sell it - so the said strategy might not be entirely stupid (apart from the idealistic motive of strengthening the network).
The same is true, if you are mining at a profit. Why not keep all the Bitcoin, if you still have enough fiat to cover your electricity bill?
ya.ya.yo!