Find a local cycling club and ride in the groups. Start with the slower folks and move up as you get used to riding in a group. Learn the protocols of group riding, taking pulls, pulling off, etc….. group riding always makes you faster as you have to respond to others, at movements when you feel like you want to slow down, etc…,

Practice doing ”bricks” which are the quick transitions from the bike to the run, it gets your legs adjusted to the different muscle uses. In other words, after you’ve done a 40-50 mile hard group ride, throw on your running shoes and go do a 5 mile run.