There are many aspects of a photograph that can be fixed or saved in post-production; exposure, white balance, and even to a certain extent composition (via cropping, etc), but not focus.
It doesn’t matter how much you increase the clarity, or sharpen the image . . . it will never be the same as having really captured it, and it will always be evident. I’d like to write a post and give you a guaranteed, fail-proof method of ensuring your images are always in focus, but unfortunately no such method exists.
You may try using an autofocus mode when starting out, but even this restricts you to key focal points and is still likely to not always pick up on the specific points within the image that you want to be in focus.
The only real way to improve your photography and ability to capture images in perfect focus . . . is practice.
To ensure that you never miss a shot and always capture it in perfect focus, lots of practice is imperative. You should practice until you are able to change focal point subconsciously. It's important to know instinctively which way to rotate the lens, and by how much.
A fantastic way to really familiarise yourself (especially if still relatively new to photography) with your camera and manually focusing is to spend time looking through the camera without taking photographs. Practice focusing on one object and then another further away; varying the subject and the focal length . . . until you can do it without thinking.
Understanding how to manually focus and becoming proficient is one of the most important and fundamental skills in photography, and one that you should be intent on mastering – afterall, the focal point of an image is what really emphasises the subject, gives the image impact, astounds the audience and is one of the only aspects of a photograph that cannot be fixed post-production.