Sorry, but it's really difficult to more-or-less time the market. That's why so many miners insta-dump and hope that the price they get averages out over time.

The only way out, as others have suggested, is to mine a coin you examined carefully for growth potential and hold what you earn. Then, mining's a lot like a long-term investment. There's a side benefit to playing the mining game this way: as a "dedicated miner," you'll make fast friends in the community of the coin you're mining. These days, with multi-pools running rampant all over the place, a dedicated miner is a real asset to the coin. The community will recognize it - and you!