I don't know if there could be the best investment strategy but if you are only looking for a long term investment just like what you have said, holding our coins until the moment you have meet your desired profit is the only best option for me . no need to have a strategy i don't want to make it more complicated though
There is nothing wrong in holding your coins as it is less risky . That way the chances of you earning a profit is high but if you want to grow your profits you need a long amount of time or the longer the waiting time the higher the profit . It is not guaranteed but it is the prediction that is most likely to happen .
Since OP is looking for a strategy . You have to be first aware that it is much risky compared to the hold technique . My advice is to trade your bitcoins to fiat or bitcoin to altcoins and much better to day trade .