Give lavender plenty of room to spread out with 2 to 3 feet between bushes.
6 to 8 hours of sun and good drainage is a must.
Lavender needs alkaline soil with a ph of 6.5 or higher. (if your soil is too acidic you will need to amend the soil with lime)
Mix composted chicken manure and bone meal for fertilizer into the soil for a natural boost.
Mulch with sand and/or oyster shells.  Sand reflects light back up to the plant creating more heat. Heat creates more frequent blooms.
Plan on limited flowers the first year. Many more flowers from the second year onward.

Remember, Lavender is a perennial woody evergreen shrub and will die back in northen climates.  In Spring, your plant will put out new growth from the shrubby stalks.  As with any perennial shrub...Be patient!!! The old rule of thumb about perennials is that the first year the plant sleeps, the second year it creeps, and the third year the plant leaps. So patience is a must. Your plant will not spread like a vine...but will keep its shape as a shrub and increase in size each year. Lavender does not like to be transplanted and never try to divide the plant. You will surely kill your beloved lavender. Reproduction should be accomplished thru vegetative cuttings or layering. (Layering can be achieved by slightly bruising a stalk or burying/covering the stalk with soil and in a few weeks/months you will see new growth coming forth from the covered branch.  Then you may carefully use a shovel or sharp tool to chop off the new plant to relocate.)