Here’s a big question, one you kind a need to consider before sitting down to start your story. What’s going to move the story along? Why will people keep reading? Are they going to like the characters and keep reading to find out what happens to them or are they going to get caught up in the situation and need to find out the resolution, even if they may not like the characters? Yes, it is possible to do a combination of both.
Why is this important? Because it tells you from the beginning what type of thing you need to do or focus on.
For example, most romances are character driven, people read to find out what happens to the people, and the people in these stories are likeable. You have to like the people enough to care what happens to them. On the other hand many mysteries are plot driven, it’s all (or mostly) about the events and solving the crime, the people in these are not necessarily likeable. You can have a detective that people don’t like but they’ll still read to find out what really happened to the victim (if you do it right.)
Once you know which element drives your story, you know which to focus on. I’m not saying that both elements don’t need your attention, but if you’ve got a plot driven story, and you focus on the next step in that story, then you won’t have to spend as much energy on your characters. The characters will react (and some of that will come with practice) to the situation naturally, and often you don’t really have to think about it consciously as the story unfolds, things seem to just happen.