Consider pretty much any issue and there is big fat core of common ground, but typically the debate is around how to best address that issue - what is the best approach, do we tackle this problem now or do we tackle that other problem first, will this path lead to bad unintended consequences, etc.
Immigration. Most people have a pretty favorable view of immigration and immigrants - pretty much everyone has an immigrant story in their background. The debate is more on the requirements to be let in, especially in cases where there is an established legal process and someone doesn't follow that process.
Taxes. Few people want to pay more than is needed. Everyone wants taxation to be fair. It's not hard to get people to admit that they see a lot of good can come from the proper use of taxes. The debate is more about tax rates, where taxes should be spent, etc.
Abortion. A huge majority of Americans do not like the idea of completely restriction-free abortions and quite a few people have concerns that, pre-birth, that thing inside the mother is a person to some degree or another. Simultaneously a huge majority of Americans do not like the idea of the government exerting control and getting involved in people's lives any more than it should.
Gun control, the economy, national defense, education, the climate. It goes on and on - name any issue and there's a ton of common ground. For people who are interested in progress and solving problems, it's ripe with opportunity.