Keep writing!!! Finish projects. Don't have a lot of half finished projects sitting around indefinitely.
Give yourself permission to write badly; you can always edit it later. Finished is better than perfect.
Your writing will automatically improve as you write more. To show yourself that this is true, compare what you are writing to what you wrote a year or two ago.
Don't be a slave of your moods. Learn to write on a schedule to complete projects. "Inspiration" is overrated and will happen a lot more often if you develop discipline.
When you work on a project, during a scheduled writing session, quit while you are ahead instead of writing until you burn out. Make notes for your next session instead of writing until you cannot continue. That way, you will feel eager to begin again.
Read Stephen King's book On Writing. And use the famous book The Elements of Style by Strunk & White.
Remember that the key difference between a professional and an amateur is that amateurs write to "express my feelings," while professionals focus on the reader's feelings and perceptions. The therapeutic effect on one's feelings is an automatic byproduct to a professional writer, something they enjoy but not something they focus on.
Seminars, classes, lessons, groups, writing circles etc. are not necessary. However, if you honestly feel helped or supported or less lonely doing these things, I won't argue with you; do what helps you. Just know they are not, strictly speaking, a necessity for every writer.
I remember how nervous I felt when I walked into my first creative writing class. That's because I was the teacher.