There are many ways your farm could diversify, the most obvious are tourism (Glamping, B&B etc.) through to Workshops, Offices, Storage or setting up a Wedding Venue, or simply marketing a field for parties.
Innovative uses of farms include green burials and green gyms.
The most important thing is research. Understand your locality, your market opportunity, and how a diversification is going to benefit (or detract from) your farm and your family.
A great place to start your research is The Business Barn, which has tons of advice and case studies from deer farming to fashions to dog agility.
Common questions on diversification are answered in this article published in Farmers Guardian and written by Hannah Moule.