I'm currently growing some lavender from seed and I was wondering if I should go ahead a prune it. I know with basil it helps with improving yields and bushiness but I'm not sure if I should prune lavender as aggressively or if it's even necessary (all the lavender on google images I see look like they have a lot of long stems, hence the confusion).
Lavender is a plant that can get straggly if it's not pruned, but it's a small perennial shrub, so its needs are very different from basil which is an herbaceous annual.
Essentially, you allow lavender to grow until it's reached the size you want for the place you've planted it. Then, every year after that, you cut it back by about ⅓ of its size; it will grow back to the original size during the following growing season. You generally do this after it has finished flowering in autumn to tidy up the dead flowers, but you can also do it in early spring before new growth starts. I use a garden shears to get mine to roughly the shape that I want, and a pair of bypass pruners for trimming any old wood that the shears can't handle easily.
Lavender will recover if cut back to old wood, so you can also use this as an opportunity to shape the plant if desired, cutting it back more in places that are overgrown.
Since you're growing it from seed, you won't need to do it for at least a couple of years. Pinching out the growing tip can encourage the young plant to become bushier, but lavender will generally do that on its own.
Every plant and tree can use a bit of pruning. The rules pertain mostly to when you can safely prune based on where you are, whether you should prune soft wood versus hard wood, etc.
Old gardening tales aside, nowadays, sites like this and others help us quite a bit. I have definitely made pruning and repotting mistakes and lost some plants along the way, so be prepared for that to happen, at least to a small enough percentage.
All said, the rules for lavender are quite easy, assuming this is the regular kind. Wait till summer is close to ending (check your zone for when this is) and then cut them down. Older lavenders will re-shoot easily than younger ones, so if this is their first year, I'd wait.
Hope that helps.
There are some pruning rules that must be acknowledged regarding lavender - certainly I agree don't prune until they've flowered the first time, then clip over the bush with a pair of shears or pruners, taking a tiny amount of foliage (less than an inch if they flower this year) at the same time. Subsequently, they should actually be pruned twice a year, immediately after the main flowering in late spring/early summer (varies according to region) and then again very late summer or early fall. Each time you clip back, you should take a small amount of foliage - in the plant's second year, take a good inch of foliage each time. The reason for doing this is because lavender is one of those plants that does not respond to pruning of old wood, and hard pruning back to old wood of a more mature specimen (over 3 years) may well kill the bush. Therefore, to prevent leggy, woody growth over time for as long as possible, it's best to prune twice a year. Even so, the average lavender bush will inevitably become woody and leggy after five years, and are frequently replaced between 5-8 years. It is, though, easy to raise cuttings yourself from the plant for replacement purposes.