For me, am not yet a trader, but read and have a little knowledge about trading. So, for the little coins I have, I sell it when there is a little rise or when I need it in cash. To every trader, they sell when there is a rise in the price of the coin they hold.
That is the right thing to do as you cannot afford to hold altcoin for a long time as price can dump at any time and in that case you are likely to sell at lower price which will not be profitable for you so sell it when you are making at least some profits as you can buy it back at the dip.