With difficulty increases, you get less return from your mining so in theory, based on the fundamentals, the price should drop. However, what tends to happen is that miners perceive that they need more hashing power to counteract the difficulty increase, so their demand drives the price higher. There's usually some volatility in price as fundamentalists sell and optimists buy, so if you're careful it is sometimes possible to sell high and buy low if you get your timing right. Conversely, some people have got that wrong, misjudged the situation, sold low thinking it would drop and were forced to buy back in higher when miner demand outstripped the selling pressure.

You normally hear people moaning on threads like this when they get it wrong. You need to make the decision why you're using a product like CEX, is it to mine, to trade or both. Being clear about that will help optimize your strategy.