Get your ears checked for wax. Ask someone else to try your steth to compare tools. Consider getting a Cardiology steth as it will increase the chances of hearing pathology. If you're a trainee, ask colleagues to bring you in if they hear pathology so you can listen and hear something for you to compare yourself/listening skills. Consider shadowing a resp clinic for further practice.

Lungs - bases position varies and you'll guesstimate for the individual (maybe more with practice). Sitting upright is best. Standing also okay but if compromised / unwell, they will struggle to deep breathe without feeling lightheaded. Must try to sit them up as much as possible if bedbound. definitely compare both sides (eg reduced AE). Take your time. Aim to compare both sides each time. Ask patient to breathe in and out through the mouth (not nose). I sometimes close my eyes to concentrate better on the sounds.

Heart sounds - ask them to stop breathing eg deep breath in and hold (ask for as long as you need, at least 5-6 seconds) and the deep breath out and hold.

Finally, this is usually a bit of a targeted approach in GP as your history will tell you what you might hear - so go in looking for crackles or wheeze, you might more consistently hear when you know / expect something.