Holding bitcoins for a long time is probably a good idea especially if you bought in at a good price. With that said, you can always buy bitcoins and just keep it on a wallet that isn't connected to the internet at most times so that you will be sure that you'll be keeping your coins in a safe place and that no one will hack or compromise your money. I've been doing the same thing for 2 years now and so far it only nets me profits most of the time.
Holding them for a certain point of a time is a good move to make but
[1]if you will never sell your bitcoins then how you gonna enjoy the profits? Even I prefer to hold my coins but won't hesitate in selling them when price goes higher then my entry price and giving me an opportunity to make profits as
[2]I can re buy them when price falls in future and I think that is the best way to make profits from bitcoins as we are investing our money into it to get some profits so we should not miss an opportunity to sell them at a right time.
[1] Just wait for bitcoins to become mainstream. Once it goes mainstream, the merchants are already accepting it and the price has already skyrocketed. By that time, not only have you made tons of profits, but you can also finally be able to buy using your bitcoins without converting them to fiat first.
[2] See, that's kind of the problem which is why most of us don't sell our bitcoins at all. You sold your coins today, and then tomorrow you'd see it growing even more. You hold your coins today, and then tomorrow you'd see the price is decreasing. The price is so volatile that no matter which move you do, there'd be a better thing to do. So most of us (or at least I think) just hold our coins and then sell them later when we actually need money.
tl;dr: Selling right now makes you lose the opportunity to sell at an even greater price.