Working for this small Parisian design agency as a designer, I learned to adapt theorical methodologies (when to conduct user interviews, how to use flow mapping...) to real-products situations. 

I worked on several products and projects, sometimes focusing on wireframes production, sometimes conducting user interviews and user tests, sometimes building UI kits. 

I picked up some valuable insights during my first year (and a half 👶🏻) as a designer :

• UI design mistakes catch the eye. Don't try to reinvent the wheel by confusing creativity and design : they need each other, but are not the same. 
• UX design methodologies can't always be applied as expected. They need adaptive intelligence : focus on user contact when they are available, gather data though unconventional means, use time-effective deliverables when possible... And keep in mind assumptions that were made without being validated, they will need special attention when ressources are available.