Many considerations come to mind when choosing the wedding day:

Season
indoor, outdoor wedding/reception; weather for honeymoon destination; holidays for family gatherings

Education
graduation; internships; exams, boards, etc.

Financial
bride and groom paying for wedding; need to save money; family needs to budget money

Family
another wedding planned; medical issues (illness or operations); anniversaries, births, deaths and divorces

Special
availability of specific venue for ceremony or reception

Situation
must have a particular vendor; must have a particular minister

Career/Work
vacation time; work load and special projects; military obligations

After these areas are visited, you and your fiancé will need to clear dates with both families. Choose three possible dates so you can be flexible when working with facilities and vendors.

If there is a special "must have" facility or vendor, book it now so your other plans will focus around your choice.