The award notice is the starting gun, not a formality
When you get the award notice, read it slowly. It states the contract number, the period of performance, the total value, and the specific document set that now governs your work, usually your final proposal plus whatever the government changed during negotiations. Everything after this point is measured against those documents, not against the pitch you remember making.
The kickoff or post-award conference
Many contracts open with a kickoff call or post-award conference, sometimes required by the contract, sometimes just customary. This is where the government walks through reporting requirements, points of contact, and administrative details that did not make it into the solicitation. Show up prepared to take notes, not to renegotiate anything. If no one schedules one, ask your contracting officer whether the agency wants one.
Learn who can tell you what to do
Two people matter most, and they are not interchangeable. The contracting officer (CO) is the only person with legal authority to change your contract, in other words to add scope, adjust price, or extend time. The contracting officer's representative (COR), if one is assigned, handles day to day technical oversight: reviewing your work, answering questions, confirming deliverables arrived. A COR can tell you your report needs more detail. A COR cannot tell you to do work the contract does not cover. Only the CO can put that in writing. Learn both names in week one, and learn which one you are actually talking to on any given email.
Get into the invoicing system
You cannot get paid by sending a PDF. Most federal agencies require invoices through a designated electronic system, PIEE for the Department of Defense, others vary by agency. Getting an account set up, verified, and linked to your contract can take longer than people expect, so start in week one rather than waiting until your first invoice is due. More on this in getting paid.
Read the contract again, as the person doing it
You read this contract as a bidder, looking for reasons to say yes. Read it again now as the performer, looking for every date, format, and deliverable it actually requires. The proposal you wrote to win and the performance work statement you now have to execute are not always identical in tone, mostly because a proposal sells and a requirement instructs.
Build your deliverable calendar
Pull every due date out of the contract, reports, meetings, invoices, option decision points, and put them on one calendar before your first week ends. Federal contracts rarely surprise you with a deadline; they bury it in a paragraph on page 40 and expect you to have found it. A missed deliverable is one of the fastest ways to a poor mark on your next CPARS report.