Don't do it. seriously unless they are one of the few incredibly skilled players going into ranked immediately at 30 is a horrible idea. Honestly they are likely not ready yet to get anything past b5 once they get a few matches done after the provisional matches. I've been down that road already and it wasn't a fun trip.
But to be quite honest b5 has had some of the more enjoyable games for me. and it's a bit of a dick way to think but being down there you can see what kind of mistakes to try to not make. You learn but you lose a hell of a lot.
And to be quite honest ranked and normal matches really aren't all that different in the low elos. I've seen people trying harder in normal games than in any of my ranked games. If you insist on rushing into ranked then play what you know and play it the way you play it best. ranked is not the time to experiment.
One last note. Please practice every role before going into ranked. There are already enough people down here who suck at any role other than one and possibly two. Better to be mediocre in all roles than great in one and never get to play it.