Be a Historian. It's easy to think why would the government want to go with a new, unproven contractor when no one knows the project better than us? Consequently, it is easy for incumbents to respond to proposals with what has worked in the past. I've seen this happen on multi-million dollar RFPs. And, the incumbent lost. As an incumbent contractor, you must remain innovative in your approach.
Ignore Your Competition. Every challenger's number one priority is to unseat you and call into doubt your ability to continue the project. They will claim that you use an outdated approach, your solution lacks features and functionality, and they can do a better job for less money. As the incumbent, it is imperative that you address these threats head on by showcasing your value proposition, a roadmap for future success and remaining price competitive.
Be Overly Confident. Incumbent contractors can convince themselves that the government customer loves them. If no one has complained, the contractor could fall into the trap that its performance is meeting or exceeding expectations. First, don't become complacent and take your contract for granted. Second, the last time I looked, evaluation factors didn't include love, admiration, or fondness. So, even if the government does love you, remember to remain aware of your contract, performance, and most importantly, your government customer.
Don't forget OCIs. Incumbent status alone is insufficient to create an organizational conflict of interest (OCI). But, as an incumbent contractor you need to be aware of what could be considered an unfair advantage. Your competitors are paying attention. You can't control how the government will proceed with a procurement. But, as a contractor, you can act with integrity and be mindful of circumstances that could call into question the fairness of the re-bid.