1: One of the most important things you can do to improve your 3D modelling skills is to look at other artist work. To do this you should sign up to something like art-station or ketch fab and take note, many artists will share there preferred methods and techniques and can be a vital part of your learning and development. So always look out how others have created something before you begin it could save you a lot of time further on down the line.
2: You have to init to win it, you will need to be modelling regularly. I would suggest that you try to fit in small projects each week, keep them simple and constrain the amount of time you have to complete them. This will help get you modelling a verity of different models which will need different techniques to complete.
3: Model using different software packages, although the interfaces will be different you will need to test how well you can apply your 3D modelling techniques in different situations.
4: Motivate yourself, if any of the above does not motivate you then try to find something that will help, some times its fun to attempt to recreate pieces from your favourite games, video or even books.
5: Model from reference and real-world objects, this will help you develop a better understanding of how to construct your models in 3D.