I waste a lot of time not coding. Typical work involves many activities, that are process related chores, meetings and etc, so only a fraction of time can be spent on coding and working on a feature. I find it important that you should try to squeeze most out of this time as possible.
I try to understand the product feature and its use cases before I begin coding on a feature. In an ideal world, your product owner will write a perfect story that doesn't require any edits whatsoever. This never happens. Product owners are humans and they will usually write an insufficient story when the stories are sufficiently large and complicated. Developers must be able to wear the product owner's hat to come up with the rest of the acceptance requirements for a story. Try to come up with what makes sense and what doesn't make sense about the story. While you are trying to come up with what makes sense, bring it up with your product owner to see if some additional acceptance criteria needs to be added. When things don't make sense in the story, also bring it up with product owner sooner rather than later.
Here's another thing I do before I begin coding. I spend a good length of time thinking about the software design of the feature. Explore how each acceptances in the story can be mapped to your software design. Your code builds on top of other code you wrote. Code you write has inertia. Early on during the coding phase, you can make small and large changes without much trouble. You are nimble when your code for the feature isn't large yet. But when you have to change the software design later on down the road, changing your existing code that has grown larger is way more difficult. There are many more moving parts and each changes you have to make in your code will need to make multiplicative changes across your code base. Also engage your teammates in brainstorming session and pick their brains on how they think the code should look.
After you are completed with coding, have a rigorous code review with your coworker. I was wrong about this before. I have been doing more lenient code review that left quite a room for disagreement. Be respectful in your tone and watch out for strong language. Messages do not get understood best over the web, especially when that message is about criticizing your code. This code review should be contrasted with nitpicking. It's not about trying to inject your preference for the code. It should be about writing good code.