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First of all you need to decide what you want to be? Do you want to be a trader or a holder? If you want to become a holder then you need to buy at a time in which the price is relatively low and then hold for as long as you can, probably years and if you can decades.
However by your post it seems this is not for you because a small drop in the price made you sell your coins, so the other option is to become a trader, one possibility is that whenever you see a correction that goes above a certain percentage that is when you chose to sell, this will protect your capital in the case the price keeps going down and it could be a good moment to take profits.
Selling on a small drop doesnt mean that he isnt a hodler yet anyone can really be considered one but the length of time on where they do tend to hold of is what make the difference.
Trading up actively isnt something that someone could easily able to pull it off thats why majority of them do end up on holding for long term rather than on playing with some moving price
actively in the market.
When to take profit into your bitcoin holding? As long you do see greens or gains and that what matter most, neither if you do just simply hold or do make some active trades.
I suppose that we must have different definitions of what it means to be a holder because at least to me a holder is someone that is able to keep their coins for a long time despite the price of their coins moving against him in a significant way, the point of being a long term holder is to keep your coins for long enough to guarantee your profits and if you sell them as soon as there is a small correction that goes against you I think you cannot consider yourself as a holder.
They'll be closer to be a swing trader or a positional trader and while you can make money with those two different styles of trading the skills necessary in order to do so are completely different.