The Semi-Sextile is a geometric aspect between two planets that are at roughly 30 degrees apart (give or take an orb of a few degrees). This aspect indicates energy that could be annoying or mildly positive, which may depend on the planets involved. The annoying nature of the energy may be subtle and therefore not easily understood. Getting the planetary energies to work together requires flexibility and open-mindedness. It helps to increase your awareness of what is happening around you and be willing to think "outside the box."
In a natal chart the person may develop a greater appreciation for the intricacies and complexities of life where the two planets are involved, as opposed to seeing life in all-or-nothing, polarized terms. On the other hand, the ability to see the subtleties and shades of grey can also make it difficult to clarify what the person is seeing.
Planets in semi-sextile are typically one sign apart. This means the two signs have no qualities in common, even though they are "next door neighbours." Like the quincunx, they have different and incompatible elements, different modalities and different polarities. In the case of an out-of-sign aspect, it may soften the irritation somewhat, since it would involve signs that are either conjunct or sextile to each other, giving them a bit of common ground. On the other hand, this might also muddy the aligned energy of the conjunction or the creative, cooperative energy of the sextile.