I typically will just hold my breath (I can do that for several minutes thanks to all the freediving I used to do) and then when I’m clear of them I’ll start breathing again. If you absolutely cannot do that for whatever reason, your nose has these little hairs that will trap some of the germs like a filter.

When someones sneezes or coughs it’ll produce an aerosol similar to spraying Febreze in one direction, the larger droplets reaching approximately 6 feet/2 meters. It’ll be more concentrated in the direction they coughed or sneezed, and most concentrated right next to them. This can be affected by wind, so try to avoid standing directly downwind of someone who is coughing or sneezing.

Taking shorter breaths would mean less contaminated air is entering your body per breath (and less CO2 is leaving) but you also need that air and also to remove CO2, so after a while your body would start to make you breathe faster or deeper to compensate. Of course, shallow breathing or not wouldn’t matter as much as wearing a mask will.