What an agent does for their clients can sometimes seem like a mysterious thing to those who don't have one, or have just recently landed one. Agents are people~oh pick your jaw up, really they are~and therefore each one is different in the way they operate. However, there are some similarities in what you as a writer can expect from your agent. Most agents are actively seeking new clients at some point in their career. This is where you come in. But once you've been picked up, don't forget that your agent may still be seeking clients, which takes up a lot of their time. Imagine wading through a thousand queries a month. That's thirty three a day. Now you know why some send out form letters.
After you've signed with an agent they will probably critique your manuscript and make suggestions to improve it. This means they have to read it thoroughly, probably more than once, and will most likely pass it on to a second reader within their agency, another agent or an intern. More eyes means less mistakes or issues are overlooked. This takes up your agent's time and don't forget that you aren't the only client they have. They're critiquing the work of every one of their clients at some point.
You're going to have questions for your agent, a lot of them if this is your first book or first time being represented. That's all right, good in fact. You can't learn if you don't ask. Just about every agent out there encourages their clients to keep an open line of communication. However, try not to flood them with phone calls or emails. How much is too much? Well first, if you have a question you shouldn't be afraid to ask. That's part of what they're there for. While editing your manuscript per their critique you may be talking weekly, or sometimes even several days in a row. Once the editing is completed and they've accepted your manuscript as ready for editors, then communication is going to slow down. Don't panic. When there's news to share, you'll be the first person they tell, trust me.
It may feel like once your agent is happy with the manuscript and has submitted it to editors that their job is over. That couldn't be farther from the truth. Submitting to editors is probably the least of their work load but it isn't always as simple as sending out a letter to the editors they think might be interested. There are dozens upon dozens of publishing houses out there and your agent has to know what each of them are looking for and who they are. This takes work, lunches, meetings, phone calls, and emails.
Remember next time you're getting impatient or worried that your agent has forgotten about you, it isn't all cocktails and tropical vacations. They're working hard for you and every one of their clients. Relax, let them do their job. Check out this great article by Writer's Digest on 5 Myths You Shouldn't Believe About Agents: http://writersdigest.com/article/5-myths-you-shouldnt-believe-about-agents