Here is some words form CliffNotes.
Lobbying efforts are directed primarily at the national level: committees of Congress that consider legislation, administrative agencies that are responsible for writing or enforcing regulations, and executive departments. Lobbyists depend on their personal relationships with members of Congress and the executive branch, which are based on keeping in regular contact. Many lobbyists have served in government themselves. This means they have worked, in some cases for years, with the very people they are now lobbying, and this experience gives them invaluable insights into how things are accomplished in Washington.
The critical legislative work in Congress takes place in committees. Lobbyists testify at committee hearings, provide the staff with information, and, more frequently than most people realize, actually write the legislation. They are sophisticated professionals and do not simply say to senators, "Vote for this bill or else," but instead explain why the bill is important to their constituency as well as what impact it will have in the senator's state. A lobbyist may have a politically connected member of the interest group contact the senator.
Important public policy decisions are made by regulatory agencies such as the Federal Communications Commission (FCC). Lobbyists or interest-group lawyers, particularly those representing corporations and trade associations, use the same tactics with agencies as they do with Congress. Developing regulations is a multistep process that involves initial drafting, hearings and submission of comments, and the issuance of final rules. Interest groups are involved in all stages: They testify before administrative hearings, submit comments or file briefs, and draft the regulations their clients are required to operate under.
This is NOT my own work. It is the work of CliffNotes.