Men and women, even though they try their best, often can't relax until the second date. There's a chance that you didn't get to see who they really are because they were distracted by their own nervousness or events of the day.
In It's Just Lunch's e-book "20 Years of First Dates", one-third of surveyed singles reported that they have had a bad or lukewarm date lead to a longer term relationship. If the other person shows interest in going out again, consider saying yes. There's a chance they see something you don't and it may pay off for both of you.
If you agree to a second date, change things up by turning the second date into a physical activity. Many people find it easier to open up and connect with someone when they are moving around.
Looking for second date activity inspiration? In an article by Marie Claire, "51 Second Date Ideas," some of the ideas included making ice cream, going on a picnic, hitting the local bowling alley, picking fruit at a local farm, go wine tasting or visiting a museum. Most of the suggested ideas were low on time investment but could produce giant results in the chemistry department.
A second date may be just want the two of you needed to tap into chemistry and make a more solid connection.