Sherlock Holmes did this using the tips above. I don’t know how effective fictional advice is for this, but he just paid attention to every single detail. Didn’t let anything escape his grasp. After a while, it just becomes second nature.
Something my friends and I do to for fun is go into restaurants and try and notice everything. Then while we’re eating, one of us will ask the others a question about the restaurant, such as “what did it smell like when we came in””, or “how many lights are there above the cash register””. We can even get mean sometimes, asking questions like “What is the brand of beer on the second tap from the cashier’s side?”. I’m sorry to confess we stole it from Psych, but it’s well worth doing. Great game, and a great way to improve your powers of observation.
<possible tangent> The second thing I do is occassionaly when I’m feeling really stressed I’ll close my eyes for a moment and ask myself exactly what my other senses are feeling. For me at least, vision is such a dominatn sense that all the others tend to fall by the wayside, so by closing my eyes, aka “getting rid of them” @mammal I can get a much fuller sensory experience than with them open. It works especially well outside, of course, but inside it can help identify unpleasant and stress causing smells and noises in your domicile. It’s certainly helped me when I know I’m feeling stressed to identify the cause of it. </ possible tangent>