I went back to school at that age and here is my advice:

1. Learn and try to apply what you're learning, especially if you're currently working in the field. I would learn about business plans and the write a business plan for the company I was working for.
2. In my experience no one cares about your GPA. I was straight A's all through my bachelors and stressed the fuck out. In my Master's program I aimed for Bs. Got mostly As anyways (that rhymes) but work/life/school balance was much better.
3. I had to work to support a family as I went back to school. A ton of stress. I decided to only work on homework the day before it was due. WHAT? That's crazy. Well, my natural inclination is to procrastinate and I found that I produced better work when a looming deadline forced me to be succinct and clear. I used ONENOTE through out the week to write notes from what I studied (I did study) and work on my outline of any papers due. I didn't event try to write until the day before...sleep on it, rewrite.
4. Create an organization system that works for you. If I had a 6k paper due in three days, the first day I would skim the reading for an overview of the material. I would then create a working thesis, write my outline, then focus my studying on the outline of said paper. Take notes in ONENOTE. When it was time to finish the paper all my notes and source links were in the outline of how I was going to write my paper. This is the system that worked for me I was I was relentless in following the system. Towards the end I could ace an assignment with four hours of work.
5. ONENOTE...This saved my butt. There is something so stress relieving about writing a thought or note down and then being able to let it go. Also, things were able to percolate in my brain and I spent the week just mulling things over and drawing correlations passively. With a phone app and cloud based, no matter where I was I could jot down some thought or idea, it was safe, and I could eliminate a lot of stress come crunch time.