How to prevent nose from pointing down when I smile, advice?

Without photos, I can only comment in a general way. But, both Botox (as well as the other neuromodulators, Dysport and Xeomin), which works to decrease hyperkinetic motion of the facial muscles, can help to diminish the kind of downward motion of the nasal tip with smiling that you seem to be describing. It usually only takes a microdroplet or two placed right at the junction of the upper lip and the center of the columella to achieve sufficient damping of the downwardly pulling muscle responsible. When there is a downward droop of the nasal tip at rest, which you say is not present here, fillers placed in that same location can be helpful in elevating the tip. Make sure that you consult with a board certified aesthetic physician. Best of luck.

In general, when somebody's nasal tip drops with smiling, rhinoplasty surgery is necessary to permanently lift the nasal tip. If you would like a more concise evaluation of your condition, please consider asking your question with photographs. Thank you. Sincerely, Dr. Joseph

although it looks like the tip plunges when you smile it's actually a complex illusion. The nostrils pull up, the lip shortens, there is little actual drop of the tip. There's an article on this on my websiteBotox and restylane fillers in the columella might help a little, they are reversible. A rhinoplasty with a tip graft would help more but is not perfect