This might be an interesting read for you:
http://growweedeasy.com/how-do-THC-and-CBD-relate-to-cannabis-potency
The only thing I can suggest is get some strains that are high in CDB, there are some good ones on attitude, Violator Kush I think is a good one...
As for increasing CBD levels, I've heard that leaving the plants to mature for a bit longer helps, once you have amber trichs let it go to something like 60-70% amber 40-30% Cloudy, but without lab equipment or reading studies I can't say whether it's entirely true
EDIT: sorry

done a few of these edits, this passage from that thread will help you the most:
"Another way to help control the amount of THC and CBD in your plant is to choose the right time to harvest your plant. You can pick the right time to harvest if you watch the trichomes (also known as crystals or resin glands, basically, it's the glittery stuff your see on your marijuana buds). You tend to get the highest overall THC levels if you harvest your plant when all the trichomes are milky/white, or they are half milky and have translucent.
f you wait to harvest your plant until 50% or more the trichomes are amber colored, then you will get a final result that has a bit less THC, but more CBD. A simpler method to determine when to harvest is to just wait until the buds have only 10% or less total white pistols/hairs. You will notice that your cannabis buds keeps growing more and more white hairs over the course of the flowering stages, but eventually (it feels like forever) the buds will stop growing new white hairs and 90% or more of the hairs will have darkened. It's hard but waiting to harvest until your cannabis plant has run it's whole life course will maximize your CBD levels. This often means keeping your cannabis in the flowering stage for a full 3-4 months. Many growers like to harvest earlier than that, but if you allow your cannabis to run its full course, you will maximize your CBD levels and your yields."