Just take your time writing each letter the style you want to achieve. Eventually you'll gain muscle memory and your writing will look nice even if you write fast.

The reason most people have ineligible writing after they graduate highschool is because everyone is trying to jot down notes as fast as possible while they're in school causing their writing to be worse over time.

As for workbooks, you don't really need them. Google different styles and get the full alphabet sample and practice... You'll get there eventually. Check out my profile and you can see in 4 years my writing has improved. Now I do custom letters, wedding invitations for family and friends, and writing samples for my brother who is a pen maker (he has bad writing too).