Top traders typically use a 'DCA' strategy, or "Dollar Cost Averaging" which is what we recommend also.
Whereas amateur traders often go 'All-In' to a trade, seasoned investors will build positions over time using multiple entries over time, to create a better overall average price, usually buy 'buying the dip.'.
This interactive Google Doc helps manage this process and auto-calculates cost, as well as helping to manage your entire portfolio of positions...