If you are hodling a good coin when and how do you sell?

Let's take XRP for example:

It's climbing pretty good now, but you have to take into account the BTC or ETH you spent to buy it.. what would be it's current value as well? Are you really in profit?

When it climbs vs the USD how do you sell it for USD? and later reinvest in BTC if BTC drops..

Do you wait for the best BTC/XRP ratio to sell?

This stuff can very confusing and frustrating to figure out..