3. GET THE EXPOSURE RIGHT
Your final image will always be better if you get the exposure right in-camera: this is just as true with a mobile camera as a DSLR. Even with all the great editing apps and filters available, exposure fundamentals remain the same. Get it right in-camera then play with it afterwards.
Small sensor cameras need light! Use the sun, get in the shade, use a piece of paper to bounce light, wait for the right light, use a flashlight or another mobile phone screen as a light source — make use of your existing knowledge to get the best light. Be patient.
Use your mobile phone camera flash as a last resort — it’s as bad if not worse as the one on your old Nikon Coolpix.