Use the camera in your phone – it has more settings than the in-app functions on iNaturalist. You can use the auto focus and exposure lock functions for macro shots. Depending on your phone this will be slightly different. On mine I tap and hold my finger over the part of the image I want the camera to focus on.
Try using a magnifying lens. You can buy special ones that connect to your cameras/phones, BUT for cheaper DIY you can also use magnifying glasses or binoculars that you find at dollar stores or already have at home.
Take lots of pictures and keep trying different angles. For example you could try to photograph from ‘downwards looking up’ on the object you are taking a picture of.
Stabilise your camera/phone. You can use special stands for your tools, or make your own (I used bull clips – just be careful not to damage your device)
Use an app to allow you to remotely trigger your phone camera (our videographer likes to use Flow Shot (Apple) and Camera Trigger (Android). Set your phone up on flowers/plants where you know there are birds or other animals and wait for them to come to you!
If plants are moving around in the wind, try holding the plant steady to decrease the movement and make it easier to focus your picture (if it is safe to do so)
Use solid backgrounds to help your camera focus on the macro subject (e.g. books or pieces of paper behind insects).
Notice the light and try to use contrasting light on your subject. If you are outside on sunny days and it's too bright, try using your shadow to help you get a better focus.