1. Get professional help. Always have a recommended entertainment lawyer review any contract (broadcasting, funding, licensing) before signing. If you can't bring a lawyer, bring an advocate to negotiation meetings. Having an experienced producer on your side during a negotiation is the next best thing to having a lawyer with you (and in some cases may even work better). It also helps to talk to other filmmakers. They may not be willing to go 'on the record' about their experiences with specific funders and broadcasters, but they might be willing to talk confidentially to other filmmakers.
2. Read any contract before you sign it. This may seem obvious, but distributors have often found filmmakers who are offering rights which it turns out they no longer own. Make sure you understand the terms of your agreement.
3. Negotiate. Realize that a negotiation is just that. It is essential as a filmmaker to try and negotiate up front the terms that work for you. If you want your film to air at a different length or you want nudity to be left as-is, ask and see if you can write those details into your contract. However, don't think you will be able to negotiate your way out of your own proposal. Some filmmakers make funding proposals based on what they think funders want, but then plan to make a different film once they have funding. Don't expect to negotiate making a 90-minute film if your proposal said it would be 60 minutes.
4. Protect your work for the long haul. Be cognizant of the time frame that a contract covers and think ahead to accommodate evolving technological platforms. Educate yourself on the various forms of broadcast rights, including digital rights. Since television and cable channels have begun broadcasting programs via the Internet, the line between Internet and broadcasting rights have certainly blurred. Many broadcasters may want 'digital rights' which includes Internet broadcasting. In some cases not having the digital rights to your film may prevent you from creating DVDs or posting your film on websites such as YouTube.
5. Keep records. Keep a paper copy of the contract on file and scan a second copy to your hard drive.