If they are currently in an elected office or have held office before you can look here
https://www.congress.gov/
and here
https://votesmart.org/
and check their voting record on bills and what bills they may have sponsored and see if you agree with the way they voted.
You can look here
https://www.opensecrets.org/
and here
SourceWatch
to find out who they swing with and who bankrolls their campaign.

The single most important thing you can do is to become familiar with the issues that concern you and compare your position to the candidates position.
And I mean really familiar.
Pay no attention to talk shows until you do this.
By talk shows I assume you mean Chris Matthews or Bill O'Reilly type shows. And then be very very careful because those people are in those jobs because they are have very persuasive personalities.
If you mean the Sunday talking heads shows then just skip it.
Indy/alt media will tell you a lot more than the big corporate news media will. Watching the big news will only tell you what happened, who said what and not much else. And they are only going to tell you what they think you might want to know... and it's all very superficial.