When it comes to swimming, the finish of your stroke probably isn't the first thing that comes to mind to work on. Most people prefer to stick to improving their kick, catch and pull, and recovery. But the finish? Definitely not at the forefront of most commonly worked on part of freestyle.
Looking back I can think of exactly one drill I did at swim practice growing up that was intended to focus on the finish of your stroke, just one. It wasn't even really a drill, and it was something I only did a handful of times at practice. All it consisted of was "an exaggerated finish" of your freestyle stroke. The set was always the same, 12 x 25s with an exaggerated finish. My coach would tell us to push straight back, as hard as we could, until our hand breached the surface of the water to start our recovery. The problem with this? It focused on an incorrect movement, and we never used it to tie into the motion of the recovery.
You want the finish of your stroke - the movement after your catch and pull - to make a "J" shaped motion away from your body. DO NOT PUSH STRAIGHT BACK. The "J" shape allows you to keep the paddle you've created during your catch/pull all the way through to the recovery of your next stroke. If you continue pushing your hand straight backwards you'll end up locking your elbow and having to pick your elbow up in order to being your recovery. Picking your elbow up puts the power of your stroke into your shoulder joint, which will lead to injury.
Not to mention that the rotation of your hips throughout your stroke works to constantly pull your hand in towards your body. Creating a "J" shaped movement with your hand will feel like you're pushing far out to the side, but it actually ends up self correcting - from the movement of your rotation - and stays pretty straight in the water. The slight outward movement at the end of the finish helps lead you smoothly into your recovery as well as keeps your paddle for as long as possible.
One of our favorite drills to focus on this movement is the Eggbeater Progression that we do on our Vasa SwimErg as well as in the water. I added the video below, feel free to follow along as you read. This progression starts off by focusing on the simple movement you make using your triceps at the end of your finish. Adding to that the next step is to practice the "J" shaped movement we're looking for in an eggbeater fashion. This allows you to feel yourself pushing back and slightly outwards from your body, making sure to keep your elbows up while doing so. Finally we put it all together into full strokes while maintaining the proper positioning you just worked on in the first two steps.
Breaking this movement down into separate movements was really hard for me, and I found out that my muscles needed to make these movements are VERY weak. Shooting this video was a bit rough for me, take a look at my face towards the end and you'll see how focused I am on proper technique...but what you can't see is how much my triceps were burning while I was "swimming" with proper positioning. Just because I've been a swimmer since I was 6 years old doesn't mean I'm perfect! My technique is something I continue to work on every time I jump in the pool.