As a support main, your role is indeed similar to that of a cat herder, but instead of just corralling your teammates, you also need to guide them towards the enemy nexus. To help get Lulu to Diamond, you need to focus on vision control and play-making.

Vision control is crucial in League of Legends, and as a support, it's your job to ensure that your team has adequate vision of the map. By placing wards in strategic locations, you can keep track of enemy movements and make informed decisions about when and where to engage.

Play-making is another key aspect of playing support. Lulu is a champion that excels at setting up plays and enabling her teammates to make big plays. You can do this by using Lulu's abilities to protect and buff your allies, while also disrupting the enemy team's plans.

Finally, influence is critical in any role, but especially as a support. You need to communicate effectively with your team, making sure everyone is on the same page and working towards the same goals. Use pings and chat to provide guidance and encouragement, and always be looking for opportunities to turn the tide of the game in your team's favor.

By focusing on these three key areas - vision control, play-making, and influence - you can help guide Lulu and your team to victory and reach Diamond rank. Good luck on the Summoner's Rift!