What normal grooming looks like
Movements are deliberate and coordinated. The spider may spend a long time cleaning and then return to normal posture.
After feeding
Grooming around the mouthparts after a meal is common. A tarantula may also clean prey residue from the legs and pedipalps.
Do not interrupt it
There is no need to touch, spray or move a normally grooming spider.
When to look closer
Loss of coordination, inability to stand, persistent twitching or obvious injury is different from deliberate grooming and deserves a closer husbandry/health assessment.