@judi’s suggestion of spelling words backwards is especially god if you want to give reader a little bit of extra information about the planet or alien. Writers have even taken a word they want and mixed up the letters. The extra meaning surfaces long after publishing, making the book a search for hidden meanings. It’s great if you want a brain-bender!
I like @Judi‘s idea. You could also just rearrange letters. A planet that is very green you could call Travend (verdant). A very blue planet Quoirtuse (turquoise).
Another idea use letters like x and z in the names.