With this team, I'm assuming that some of them play other games, but like not in a club. The more I play league, the more I can understand that many of the aspects of league can be explained by using other mediums used in entertainment and work. For example, let's say you want to focus on the meta for a week or so. Explain it like you would fantasy football or fantasy gambling. In every sport there are certain strategies and ways the game is played in the current that are better than were better in the past. Who would you rather draft in your fantasy football league today: Bart Starr in his prime, or Aaron Rodgers? Another example, many are familiar with different war concepts, such as flanking and line of sight, similar to ganking and warding.
Final thing, figure out what people like to lean towards, like give out a survey. Don't necessarily give out champion specific options, like "Do you enjoy launching projectiles at far-away targets?" (Which would be a hypercarry adc question), or at least have a semi-serious converstation, like "If you were in 'x' situation, what would you do?" Just give them lots of ground work and give them plenty of opprotunity to explore what they would enjoy about the game, whether its being unkillable (Tanky Top Lane), assassination (Midlane), Controlling the map (Jungler), being the maverick ace of the team (ADC), or keeping the entire team safe and making the biggest impacting plays (Support).
Just really get down to what they want out of the game if they are looking for an objective to league. That's all I got. If you ever want anymore verbal help, add me. My IGN is crabface5. Good Luck! Wish I could start up league team at my school.
One more thing, what would your team necessarily be doing on your team? Are there local tournaments, other schools, or online tournaments?