Also in advance of the garden party is edging the beds. Right up there with weeding (and having a good design for your garden layout in the first place), edging is one of the most satisfying and effective things to do to help the garden start to look inviting.
BEFORE: The two long beds flanking the central "runway". Clearly there's some simple geometry here, but it isn't enough just to have it suggested with a broad brush.
Cutting the grass back to the inside edge of the mowing stones is the answer.
AFTER, AT LEAST A BIT: Even before the weeding, the sweeping, the planting, the clean-up, the difference is seriously good.
Now the runway has a definite side edge. It's all of the sudden an entity, a design partner, for the huge beds on either side, not just the interstitial space between them.