My strategy is to continuously buy every month and never fail to do so. Also, I don't care what current price is, I just buy.. It's not a very smart nor is it the best strategy out there but it works long term especially with good asset selection.
Using a certain percentage of our salary is the best way in my opinion of investing into bitcoins, Buying it on a monthly basis without spending a single will ensure that you will have a large number of bitcoins and if the value hopefully goes up during the period you will notice a huge profit.