There is a difference between general strength and specific strength. You should do general strength before specific strength. I have written a lot about this topic before, just search letsrun runningart2004 strength.
In general:
1. No more than twice a week on your hard running days after your hard running and preferably after a meal and some rest.
2. Focus on compound movements for the lower body. I suggest a Cross-Arm Front Squat and a Trap Bar Deadlift because they required limited technique compared to alternatives.
3. Basic Linear Progression in 3-4 week blocks. 3 weeks of 2x weekly 2-3 x 8-12, 3 weeks of 2x weekly 3 x 5, 3 weeks of 1x a week ramping to a max set of 3. Then start more specific lifting:
4. Specific Block: Start Plyos: Single and Double Leg Hops. Quarter Depth Speed Squats: 3 x 5. KB Swings: 3 x 5. Single Leg and Explosive Variations.
5. Upper Body Stuff: Dips and Pullups are fine.
Focus on powerful force production when you lift. Not just pumping out the reps as fast as you can. You already have endurance. The point here is to build strength, power, and explosiveness that improves running economy.
Alan