Cut back hard in the spring - new growth regenerates from woody stems - this will create a more compact plant

In cold weather, lemon verbena needs to be brought inside.  It will drop its leaves when stressed with cold (don't throw the plant away; the leaves will grow back.)

It is a heavy feeder.  Give it a well-balanced water soluble fertilizer 1x month 

Keep soil moist, but not soggy

Give it as much sun as possible until it becomes too hot; then move to part shade