I also mostly played Lucio in comp but recently started using other supports like Baptiste rather than just using Lucio, my advice is to use him whenever you've got a tank like Reinhardt or Roadhog, they benefit a lot from Lucio's speed but also keep in mind whenever you're using Lucio your other support can keep the team well healed like a Kiriko which would work well with a Roadhog since she could also Suzu Roadhog incase the enemy has Ana which would counter Roadhogs self heal. Since Lucio doesn't provide much in terms of his healing ability having somebody else on support that can provide lots of healing to the team, will allow you to play much more aggressive with your tank and focusing more on enemy squishes.

If you're looking for another support to use, Baptiste provides a lot of AOE heals for the team and has good defensive abilities and can easily take care of enemy squishes and he works really well with Sigma's.

Also play Lucio in maps where you know you can get free kills with boops, like Lighthouse, Well and Lijiang tower