One subset of the words / strings often known as 'sentence connectors' (this subset also considered a subset of pragmatic markers involving both information ordering and speaker viewpoint) includes:
however; however, on reflection; mind you; still; nonetheless; nevertheless; all the same
All these words / strings are used to present two contrasting ideas. Mind you, however, on reflection, and still have a hint of reconsideration by the speaker to concede the alternative viewpoint – an afterthought. The others indicate a more planned statement of contrast (and are more formal).
Smoking is proved to be dangerous to the health. Nonetheless, 40% of
the population smoke.
Our teacher promised to take us on a field trip. However, he changed
his mind last week.
Peter was warned not to invest all of his savings in the stock market.
Nevertheless, he invested and lost everything.
You should not shirk your civic responsibility to vote. Mind you, I
Mind in the sense used here means 'bear / keep this in mind' or, more urgently, 'mind out for / that', as stated above. It is a pragmatic marker, of the attention-focusing variety.