One of the biggest blunders we all make in our writing is losing sight of logic as we write our stories. On the surface, the sequence of events may make sense to us, but to a reader, or even more specifically an editor, they may be far less forgiving. This is one of the biggest reasons, next to plain old bad writing or uneven pacing, that a book can fail to hit the mark.
When you are crafting your story, channel that person in your life (we all have at least one) that needs to know the details of everything and asks all the questions. They take nothing at face value, but need to understand the minutiae details of why and how A connects to B. Even though these elements may not be detailed in your story, they are critical for its ultimate success. For example: It's not enough to write a love story where a 17-year-old takes off, hitches a ride with a friend and follows a boy she loves across the country. It's romantic, sure, but there are niggling details that need to be addressed: How will she get home? How will she pay for it? Would her parents let her go? If not, why not? What will be the ramifications if she just takes off and how will she address them? What if the boy doesn't return her feelings? What then? Are there too many coincidences in your story that just make everything fall into place too easily? Because life isn't like that.
The stuff that makes up the meat of the story is in those details. What's the worst thing that could happen to this girl if she goes? Make sure it happens. How does she feel about the situation? Make sure it has changed and evolved by the end, and not just via an epiphany, but because of some catalyst action that makes her and her views change in a realistic way. We don't just turn our feelings for someone on and off like a light switch. They develop over time, sometimes we are in denial, sometimes it takes something painful to make us see how things really are, or maybe something has happened that can't be ignored along the way that has created different feelings for someone else.
A reader may be willing to suspend disbelief with proper world building in a science fiction or fantasy novel, but it's equally hard to pull off in a contemporary novel, because this is an actual world that your reader may be able to relate to directly. Make sure you've established traits in your characters that support them taking the actions that they do or it will be implausible and possibly make the reader unsympathetic.
Question everything, every action, every exchange between characters. Not just to see if it needs to be there to move the story along, but if it could really happen and it makes sense for it to happen with the characters you've created. First ask why they did this and what are all the possible logical outcomes. Then choose a realistic one and figure out all the realistic outcomes of that choice. It's like a giant chain based on each individual choice. But it all begins with your characters. If you don't know who your characters are, the reader certainly won't be able to connect to them either. Despite your anxiousness to throw words on a page, sit with them awhile and perhaps write some backstory so that you understand them a bit better before moving forward. Then their choices might become clearer to you.