The best method for investing in something so volatile as Bitcoin is a well known method called Dollar Cost Averaging.
Instead of say sinking $10k into Bitcoin all at once; buy $100 worth twice a week for a year.
If Bitcoin goes to the moon you won't make as much profit as if you put all $10k in at once.
But if Bitcoin goes down in price, you will be extremely happy with your strategy of Dollar Cost Averaging. You will end up owning much more Bitcoin with a much lower cost basis.
Now that you've decided your investment strategy and how much you want to invest you need to determine your exit strategy or contingency strategies.
Decide ahead of time the factors that would cause you to sell; and only sell when those factors are met.
For instance for me; I would only sell if technical problems became apparent in the Bitcoin network.
However most people their contingencies will be based on the price; for instance; that you will sell X amount at Y price. Write your contingencies down and stick to them.
I do not plan to stop accumulating for another 16 years. Regardless of the price I intend to continue buying small amounts and ever increasing my holdings until ~2032. At that point if Bitcoin is still around it is very likely to be extremely valuable