For optimum lemon flavour, I would recommend using fresh lemons (not ones that you've had sitting in your fruit bowl for weeks!) and organic ones if possible.
You have to be careful when baking with lemon juice as the acidity and lemon flavour can really vary depending on the lemons you use.
I would recommend tasting the lemon juice you're using and adjusting the amount of lemon juice you use accordingly.
For the lemon zest, make sure you use unwaxed lemons.