How do I prevent this from happening again after a botox brow lift? (Photos)

The simple answer to your question is that the Botox was not injected properly giving rise to what has been descrbed as the "Spock" (from Star Trek) or Mephistopholes arching to the lateral eyebrows. Properly injected, Botox is routinely used by experienced injectors for the a "chemical browlift" (i.e. to elevate and create the more desirable subtle, feminine upward and outward flare of the outer third of the eyebrows without created the Spock look. The use of too much Botox in the area can lead to, as in this case, loss of the desired effect. Make sure to consult with an experienced, board certified cosmetic dermatologist. Best of luck.

Dear goodgal46,
Thanks for sharing your photos. You appear to have mild upper eyelid skin excess with residual upper forehead creases in repose and asymmetric brow lift with a bit of eyelid lift improvement when elevating the brows following botox.
• It is always easier to improve a under-treated brow-forehead with botox injection with a touch more botox 2 weeks later (even if the middle brow-peak (“Spock”) or later brow-peak (“Mephisto”) appearance occurs; rather than over treat across all forehead lines developing a untreatable brow ptosis. Following brow ptosis, the botox effect will require a 3 month time for reversal.
• The explanation of why this occurs is complicated. Yes, it is partially technique but it also is changing anatomy. The more one uses botox, the more muscle fibers are quieted and therefore the combinations of facial muscles of expression change; requiring re-evaluation of where and how much to inject. You may consider a hyaluronic acid filler to the transverse lines across the forehead rather than experience brow-ptosis and brow-peaking issues like the one you have experienced.
• You are not a poor candidate for continued “botox” brow lift.
• Consider a bilateral upper eyelid lift
• If and when, the skin slides over the forehead muscle and ‘botox’ appears ineffective, consider a brow lift: PDO thread, skin-lift, endoscopic.
I hope this helps. All the best!