I usually go RB first and then decide the draft as it goes along. The order of pick depends on several factors:
1) Quality of players in each position and relative strength of players in each level
2) Scoring system (PPR, PPC, Points per yard etc.)
3) Draft Order
So for example if, in that year's QB class, the top 5 QB's are FAR more elite than remaining top 10 and if you're picking 12th in the draft, you may not have an opportunity to pick an elite QB. In that case, save the pick for a great player in another position and you can draft a GOOD QB later on in the draft.
In summary, my main strategy is to get the player rank by position and fantasy points from the previous year and evaluate their relative ranking before determining my next pick... which changes constantly over the course of the draft.