I am personally a miner, and I keep all I mine. I just sell from times to times what I need to pay for the electricity but that's all. Time said me I was right and with my predictions in the crypto-currency market, I will be right another time.
Sell enough to cover cost and your overhead. Hold on to the rest for as long as you can afford to. There is good value in playing the long game.
That is right just sell some coins to cover your expenses and also to buy or pay the things that you need in order to maintain good financial status and the rest should be kept in a cold storage like hardware wallets in order to have a good investment for the future because the price of the altcoins and also bitcoin are very unpredictable.