Write out all the team match-ups you will require over the course of a season in a spreadsheet or word processing program. Every team will play their divisional opponents twice, and their non-division opponents once. If you are using a home-and-away schedule, assign each team a home and away match for each division opponent. Give each team four home non-division games and four away non-division games as well.
Print out the match-ups.
Cut the match-ups page into slips, with one game on each slip.
Separate the slips into inter-divisional match-ups and divisional match-ups on a flat surface.
Arrange the slips in the divisional grouping into six different groups of six slips each, being sure that no team is in any group twice. This creates the six rounds of divisional match-ups for your league.
Arrange the slips in the non-divisional grouping into eight different groups of six slips each, being sure that no team is in any group twice. This creates the eight rounds of non-divisional match-ups for your league.
Record the groups in the order of your choosing, with each group representing one round of games, to create your schedule.