I just put in what I need at the moment to grow my coins, but I also cash out once I made more.
But the price is too high last months for me to take any big risks and speculate on short term.
you can also spread your investment into smaller buckets. for example, you buy right now with 25% of the money you have, and keep the rest aside in case the price goes down. it will allow you to benefit from a potential decrease. and you'll also benefit when the price does happen to go up since you bought yourself some coins. that's exactly how i have been doing it since the very beginning.