I disagree with the lucas formula, and im currently using it. It has half or 1/3rd the level K (potassium) which GH recommends. i hear will mean a potassium deficiency if you leave the plant to veg too long. Apparently Lucas only veg's for few weeks so hes off to flower fast.
http://www.hydroponics.net/learn/weekly_feeding_program_flora.asp
Alot of people use the Lucas formula for FLOWERING i have yet to get that far with it but I will be trying it!
I am currently using week 2 of the GH formula, Its at 380ppm and next week ill gradually raise it to week 3 limit.
Id recommend you start simple as fuck your first go, there are so many ways to screw it up. I was having so much trouble with my plants because my humidity was too low. EVERYONE was telling me humidity is bad, the lower the better. Well I come to find out that plants in veg love a humidity of 60%. I have trouble maintaining 40% right now but even at that level my plants are recovering fast.