Caralee - not to suggest that I'm a master at this (ha, ha), but my approach, starting back in September was to send out an average of 1 query a day. Some days I did 4 or 5. Some days I took a break and did none. I threw a very wide net, ending up querying about 100 agents. Half passed on the query. About 15 percent requested fulls or partials (5 are still out there being considered). The rest haven't responded yet, or passed via silence.
So, some have called my results encouraging. I don't really know what to call it at this point. But maybe it's a decent approach.
Another interesting, debatable topic is who you should query first. It seems intuitive to cull your dream list of agents and send to them first, since - hey - maybe one of them will love it and you'll be done querying in 24 hours.
But someone brought up above that your query/pitch tends to get sharper and more effective with practice. So after a few weeks or a month, you may have honed your best letter but already got turned down by your A list of agents.
This kind of happened with me. At least, I feel my later query letter was stronger. But I can't say there was a huge difference in the number of requests I got from either letter. And, even after two months of research, I was surprised to discover some new agents that really looked like a great fit for my book. Hence,
I don't know that it matters who you send to first.