This little piece of halacha seems like it should be obvious, but maybe that’s just me.
Don’t daven or say a bracha around a foul smell.
As a practical matter in shul, this usually relates to passing gas. If you really need to do that, go outside for a minute. Halachically, everyone around you should stop davening until the smell dissipates. So if you break wind in shul, that’s just rude. (And disrespectful, etc, etc…)
Similarly, don’t daven or make a bracha beside a trash can, bathroom, or other smelly place. I’ve seen some say that the “rule” is standing approximately 6ft away from the bathroom or a trash can. I can neither confirm nor deny, but I’m sure commenters can clarify that.
Likewise, if you notice that people in shul don’t want to daven near you, you may have a body odor issue…
potentially someone could be making a bracha over the smell you refuse to say a bracha around. Some people can't stand certain smells that others find pleasurable. For instance I can't stand vanilla or lavender. Both make me gag… while most people have positives feelings about them.
You're not supposed to, uhm, pass gas, while wearing tefillin. I think I was/ am pretty average in this department, but when I was turning bar mitzvah and this was explained to me, all I could think was "How on earth are you supposed to prevent this from happening?" Yes, the point is you should take off the tefillin, but darned if I thought that was a practical possibility. And, to be quite frank, it isn't as if you actually see people taking off their tefillin all the time.