I generally make abstract or surrealist pieces. I don't know where ideas come from, but I do a certain amount of "making things up as I go along"
Realistically, though, sci-fi and fantasy objects are based on objects we have in everyday life. If you look at sci-fi through the years, they have the era's aesthetic: The lines of 50's sci-fi are different from the 80's appeal, for example. And this is where you start to draw the imaginary stuff.
Sci-fi ships? Based off of a combination of naval ships and planes. Get reference photos and use these to guide you, adding and taking away as you see fit. Plant life on another planet? Use plants and fungus from earth as your guide. Again, get reference photos and use these to guide you, changing what you like. Want an easy way to start something more surrealist? Find 3 unrelated reference photos and combine them into one image - use a digital art program to combine them if you'd like.
Note the heavy use of reference photos: I use them whenever I want something shaped in a specific way. If I want a goldfish in a space portal, well, I look up a picture of a goldfish. If I'd like koi instead, I look it up.
Realistically, though, sci-fi and fantasy objects are based on objects we have in everyday life. If you look at sci-fi through the years, they have the era's aesthetic: The lines of 50's sci-fi are different from the 80's appeal, for example. And this is where you start to draw the imaginary stuff.
Sci-fi ships? Based off of a combination of naval ships and planes. Get reference photos and use these to guide you, adding and taking away as you see fit. Plant life on another planet? Use plants and fungus from earth as your guide. Again, get reference photos and use these to guide you, changing what you like. Want an easy way to start something more surrealist? Find 3 unrelated reference photos and combine them into one image - use a digital art program to combine them if you'd like.
Note the heavy use of reference photos: I use them whenever I want something shaped in a specific way. If I want a goldfish in a space portal, well, I look up a picture of a goldfish. If I'd like koi instead, I look it up.
(and by the way, my stuff, if you would like to see how it plays out in my work. It hasn't been updated in some time. https://www.deviantart.com/disgruntled-peon/gallery)