Well, it's sort of hard to say what tips and tricks you'd find useful without really knowing your "skill level".
That being said, some general tips off the top of my head are:
Have a color palette/ color system for characters and background - do not use the same saturation and values on both. Usually having the character have brighter, more saturated colors makes them always stand out and make sure they don't blend with the background.
Remember that the characters are viewed from the top. When drawing the sprites from the front, they sort of form a slight V shape - just general perspective goes a long way. It's not like this is any sort of a trick, just a guideline that helps me when drawing and designing sprites.
Don't have the feet at the same pixel height, even one pixel vertical difference is felt very well. One foot being slightly in front of the other gives depth and it doesn't look like the character is standing on a tightrope.
Think of how long stuff takes to create - even if you're not constrained by time, it does help to simplify. Don't make the characters too complex, noisy, full of textures. Simple is often great, from both a work pipeline and visual stand-point.
Look around, find examples of top down characters which work and which ones don't. You can learn a lot from terrible examples when you think hard about why something looks bad and how you could improve them.
Hope something can be helpful.
