There's no hard-and-fast rule, it's tempting to lock up an IDP stud linebacker to anchor your defensive lineup, and if a value comes by that's too good to pass up by all means don't. But many players are available rounds after a bigger name like Jared Allen or JPP and can offer fantasy owners similar IDP production while affording them the chance to stockpile an upside receiver, sleeper quarterback, or handcuff running back to boot. So dont be afraid to wait til later rounds and dont get stuck in an early IDP run! Linebackers usually rule IDP leagues with sack monster DE's coming in a close second. DTs are scarce and very undependable so even though they dont score the most they are usually valued pretty highly. Dont draft DBs till really late. There are exceptions to this rule who have shown themselves capable of steady IDP production over several seasons, but more often than not last year's treasure can quickly become this year's trash at the DB position. Sorry this is a block of text but hope these basic tips help you.
I drink because of the 1998 NFC championship game.
12 team big $$$ non PPR league - QB RB RB WR WR TE D K
RB: Murray, Matthews, R.Bush, D. Brown
WR: Julio Jones, Colston, VJax, Garcon
TE: Witten, Gresham