Baptists can be a mixed bunch, truly. My perspective is from the US, so I’ll give that. Forgive me if you are not in the US.
In the US, I’ve had contact with two main “types” of Baptists, Independent and Fundamental, and Southern.
Polity is “upside down” with respect to Catholic, Orthodox, and Anglican churches, The congregations recognize and legitimize the denomination (often called a “conference”) and it’s hierarchy rather than the other way around, and, in at least some respects, the pastor serves at the pleasure of the congregation and may be dismissed by a vote of church members.
“Southern” Baptists are a conservative bunch, but are often casual (at least in the suburbs of a major metropolitan area) and you are unlikely to offend them greatly in terms of dress. They may be mostly White, and the denomination officially supported slavery in the US when it was legal.
Independent, Fundamental Baptists are, well, generally independent and certainly won’t answer to a Bishop, or really anyone else but themselves! They may range from almost-Southern Baptist practice to ultraconservative groups that practice strict separation from the world and strict gender roles. Some congregations may require that women not speak and forbid them from holding any leadership roles. If you are a woman, I recommend wearing a modest dress (or skirt and shirt combo) below the knee on your first visit, as opposed to wearing pants. A few require women to cover their heads, but I highly doubt that they would pwn you for not knowing.
In either Baptist service, you may encounter what is called an “Altar Call”. Basically, the Pastor or someone else may call anyone who wishes to be “Saved” up to the front to “accept Jesus”. They may or may not baptize the person at that time, but then they believe that Baptism is a gesture of obedience, not an act that is necessary for it so they may try to get you to “accept Jesus” then send you to a doctrine class leading up to your baptism. Recognized baptism is generally required for full church membership.
If you were baptized under the age of reason, or were baptized as an adult by pouring or sprinking, the general rule is that it is not recognized, but exceptions may be made depending on local policy. If you were baptized as an adult with an immersion, it may be recognized regardless of the denomination (e.g. my Mennonite immersion baptism would be fully accepted and I could join a Southern Baptist church just by taking a class in Baptist teachings and making a profession of faith)
Baptists can be kind of pushy and anxious to “get people saved”. They generally believe that salvation cannot be lost once achieved, but do recognize that one can have the outward appearance of salvation (profession of faith and baptism) but still be unsaved because the person’s intent was not right.
There are also “American” Baptists which I really have not encountered. They may be more liberal in terms of practice or theology.
In the end, if you are a man, I’d recommend a pair of khakis and a nice business shirt and tie for the first day, and if you are a woman, a dress or skirt/blouse at least to the knee and that is not cut low. If the mark is actually higher, it won’t be terribly higher and they will probably give you the benefit of the doubt, especially if they have targeted you for conversion!
