Depends on so many factors. I think, first of all, you decide whether you have already had your maximum number of bitcoins or are still accumulating.
If accumulating, buy all the time and especially on dips. Now is not a 'dip', but it still qualifies for 'all the time'.
If divesting, sell on peaks. If you are sitting on good gains, it might be good to start selling already. Sell a total of 20% in this peak that we will be having soon.
Whether it is a peak or a dip, construct a rising exponential trendline and follow it.
Do not swing-trade or daytrade unless you know. I don't know any successful bitcoiners who daytrade.
Im still accumulating, but trying to sell on peaks to buy later cheaper, ive sold almost all at 400 but finally bought again at 500 and now i dont really know what to do, im a beginner... looks like it going up to maybe 1k i dont want to lose the train lol, neither the crash explode on my face ;-)
If you are still accumulating, don't sell! Easy as that.
Also since you are accumulating, when the crash hits, just refresh your wallet balance every 5 seconds. As long as it stays the same, you are doing good. If you scrape some cash to buy some more, you do even better.
WTF is wrong with this generation that sees a purpose in selling all that they have.. Why buy in the first place if you don't want it...