Two major red flags to look for in people
Red flag #1: Case of mentioning the exes.
For example, say you and your date are talking about each others hobbies, and then your date brings up that his or her ex loving to do the same hobby you enjoy. You shouldn’t be too concerned yet. But, if your date continuously mentions their ex more than once, you should be concerned. If someone continues to talk about their ex while you're on a date it is very disrespectful. You two are on the date to get to know each other, not bring emotional baggage into the picture.
And there is a reason why they are called exes. If your date hasn't moved on with their life and gotten over their ex while they're dating you, there is a very high probability that he or she may cheat on you with their ex. especially if they are still talking with each other on a constant basis! Some may disagree, but it's safer to completely cut off contact from your exes, unless you have a child with them of course. Not only is it completely disrespectful to your date, but it shows that you may have serious emotional baggage. And going into a serious relationship with emotional baggage is a disaster waiting to manifest itself.
Red flag #2: Sexual innuendos and remarks.
One of the worst things that can happen is if you're trying to have a decent conversation with someone is for them to keep commenting on how great a certain body area on you looks; or if they keep making sexual innuendos about having sexual relations with you soon. It may be flattering to some at first, but will become annoying and suspect if it's continuous for most people.
Be on guard for people who make sexual remarks about you or with other people surrounding you. This could very well mean that the person is mainly interested in you for sexual relations. And if you're looking for a serious relationship, this is not what you mainly want your relationship to be based on! After the fun dries out, there is no where to turn and the relationship will turn soar, resulting in a breakup and a complete waste of time.