for example watch the difficulty graph for the last 6-12months of your favoured coins
This is unfortunately a double-edged sword. If there are not many people that are aware of a coin then it is unlikely that it will increase in value or even maintain the value it already has. It's a guessing game sometimes, if you believe a coin is going to catch on then it would be wonderful to mine it before it gains attention. It's near impossible to tell which coins are going to maintain or increase in value, so I've seen too many people spend months mining a coin that becomes worthless before they get to sell it.