Yup, I would gradually increase both your running and biking. Don't be tempted to do any formal running speed work at the expense of more miles. Most experts agree that until a person has been consistently running 20-30 miles/week for at least 6 months that speed work is a recipe for injury. Most people find that simply increasing their overall mileage is where the early pace increases arise.

Brick workouts are good, too. You really need to condition your quads to transition from that bike leg back to run.

A great book to check out is Gale Bernhardt's Training Plans for Multisport Athletes. I've used this a couple of times for duathlons. She has several different distance plans and for experience levels, as well.