Here's a quick little tutorial on how to do a basic-ish top-down spacecraft using Krita. The instructions are kind of basic so it may be possible to follow along using other software.
Don't forget to turn "Horizontal Mirror Mode" on before you begin, it's a small button in the upper, right hand corner.
It takes a bit of trial and error to find a good starting point for a spaceship design, but once you have a part you like, base the rest of the spaceship off it. For instance,if you've drawn a wing you like, add various parts until you have a complete spaceship.
When you are designing the basic shape of your spaceship, don't be afraid to use cntrl+z, a lot.
Now use a light grey color and the same "sketch_ink" brush on a new layer (Press the "Insert" key to add a new layer and move it below your current layer by clicking and dragging in the layers area).
Use the light grey brush to connect the black parts of your spaceship.
Now use a somewhat darker grey brush to add some detail to your light grey layer.
Create a new layer by pressing the "Insert" key and move it above all your existing layers. Choose what colors you are going to use for your image, you may want to use contrasting colors or complimentary colors, but if you want to play it safe, use only one main color. I have chosen orange for this example.
Next decorate your black layer with interesting sci-fi type shapes that go with the shapes you have chosen for your black layer. Try to keep them the same type of shapes as your black layer, if your black layer has a lot of sharp edges, do likewise with your colored layer.
If you have only chosen one color like I have here, add some more details on top of your colored areas with a lighter or darker version of the color you chose.
Add yet another layer and move it to the top of all your layers, turn off horizontal mirror mode and draw a little shine on the cockpit area of your spacecraft to differentiate it from the rest of your spacecraft. You may use the same "sketch_ink" brush as I have done here.
And there you have it. For this tutorial the spaceship was pretty basic so you get the main technique down, but freel free to get creative, go crazy with detail, shapes, colors and shading! I hope this tutorial has helped you, thanks for reading!