Is there any suggestion to reduce staircase effect in FDM printing?

It depends on how much time or money you want to put into post-processing.

If you have reduced the layer height as much as you can, the only other steps are changing orientation and then a lot of post-processing.

If you are making hundreds of these parts, you might look into vapor smoothing, which has very smooth results: https://all3dp.com/2/abs-acetone-smoothing-3d-print-vapor-smoothing/

Vapor smoothing uses toxic vapors which is a worry, and usually requires an expensive machine, but again, if you are printing hundreds of parts, it will save thousands of man hours.

If you MUST do everything by hand and are only printing 1, then you will:
1. Sand in increasingly fine grades of sand paper,
2. Prime the part with automotive primer
3. Spray paint on top of primer.

The grades of sandpaper don't have to be exact, I usually start coarse, 100 or 200 grit, then go smoother in stages. What you are looking for is to remove the HEIGHTS of the layer lines. (The primer will fill in the VALLEYS.)

Then wash and blow away all the sanding dust.

Step 2 is use any off-the shelf automotive primer, I usually use something like this for $6: https://www.amazon.com/Rust-Oleum-2081830-Stops-12-Ounce-Primer/dp/B000V69Q58/ref=asc_df_B000V69Q58/?tag=hyprod-20&linkCode=df0&hvadid=193184886406&hvpos=&hvnetw=g&hvrand=2247779795896022680&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=1027266&hvtargid=pla-314699645483&psc=1

You only usually need 1 coat of primer.

Step 3 is paint, again, any spray can paint will work. I usually put 2-3 coats on there. Keep in mind that any coat will increase the dimensions of your part some, if it has to slide into something else.

It's actually not at all different from finishing WOOD or car parts, so if you watch any youtube tutorials on woodworking, you'll get the general idea.

Message me if you have any other questions! shuvom.ghose@stratasys.com.