No real secret here. Some people like brick training - bike followed by run repeats. Others say that bricks don't do anything but practice bleeding!!
Personally, near race season, I do this session:
Warm up on bike EZ with a few spin ups
3 miles or 9 mins quite hard on the bike (turbo is good for this)
Jump off the bike and run 1k
Rest 2 mins then repeat.
Start with 3 to 4 repeats of the bike run. Keep the bike effort constant (quite hard) but get faster on each subsequent run effort of 1k.
I start with a 4 min 1k and decrease by 10 sec on each run (or I try to!). The idea is that you have to run faster as you get more fatigued. Try short choppy strides as you start the run and then gradually lengthen your stride as you find your run rhythm.
I found the more I raced the easier it got to run after the bike. However, there are still days when no matter what, the legs are in bits and stay that way for the entire run!