Today I'm going to set the record straight.
When to Nudge...
On a Query
99.999% of the time, the answer is NEVER! There is one exception, and for that I'll quote Anna Webman of Curtis Brown LTD:
Perhaps, the only exception would be if the author receives an offer of representation or legitimate interest from an editor. In that case, if they have a specific dream agent who didn’t respond to their query, they could follow-up with that person and let them know the good news.
On a Partial
Three months. It seems like a long time, but agents have a lot of material to sift through. (A lot!) So you'll need to sit back on your heels and wait. Or better yet, jump into your next writing project.
On a Full
Hang on to your hat... six months. (Did you gasp?) SIX MONTHS. I know this seems like an eternity. And you may hear back from the agent before this allotment is up. But you need to give them a good amount of time to consider you as a client, which includes time for them to research you online.
Say agent A has your full, and agent B sends an email saying he/she likes your work but wants to talk about revisions. Is it time to nudge agent A? Surprisingly, no. At this point in your journey you are more likely to nudge them into a "no." So when should you nudge them? Only...
When You Have an Offer
It's time to pull out all the whistles and bells and nudge every agent who is considering your material. (This includes partials.) Let the agent know you've had an offer of representation, and give them at least a week to consider your material and get back to you.
The TOP SECRET Nudge
Some agents are willing to reconsider your work after you've taken time to revise it. This is especially true if he/she liked your story (or writing) well enough to offer feedback. You'll need to tread carefully, because you don't want to come across as pushy. A simple "I've revised TITLE OF BOOK and am wondering if you'd be interested in seeing the new version." This only applies to agents who have previously read a partial or full.
When to Call an Agent?
There is only one answer: WHEN THE AGENT INVITES YOU TO DO SO.
How to Nudge
Number one rule: Be polite and professional. A secret rule: Be brief. Something like, "Thank you for considering TITLE OF BOOK. I'm wondering if you've had a chance to look at it yet." Make sure your contact info is included in the email.
Things that will Help
A great place to go is the agent's page on QueryTracker.net. People leave comments about their experience submitting to the agent, and by looking at the agent's statistics you can have a rough idea of when to expect to hear from him/her.
One final note, none of these rules is set in stone. In fact, many of them vary slightly depending on each agent's particular tastes and method of operation. So always, always, always check their websites for guidelines.
I'd like to say THANK YOU to the agents who weighed in to help make this article possible!