Robert J. Sawyer claims that the best way to get an agent's attention is by writing short stories to get publication credits. He may be right, but what if I just don't feel I have any short stories in me?
Between managing one paying job, two households, family and pets, it's tricky enough keeping the novels I write on track, especially now that I've got a complete one in the shop-it-around phase, and another draft that needs substantial love and attention.
I admire people who can be so prolific with their writing. But I'm not going to panic at not having short story credits to put forward. A couple of other published authors have given me the opposite advice: focus on what you're good at and don't worry about building a portfolio.
Then again, he's won every major SF award, and I'm still schlepping to the post office with my query letters. Maybe the joke's on me. :-)
The odd thing is that I've read exactly the opposite advice: if you plan on making a career out of writing fiction, novels is the way to go. Once you've established yourself there, you'll find a market for your short stories.
Sawyer's advice might be applicable for just speculative fiction, where the short fiction arena is still thriving.
I guess the moral is "different strokes for different folks". :-)