If you want to improve your baking result for static lighting, you can use lightmass settings from this quick tip. It will increase the time of baking, but provide a much better result with fewer artifacts.
Tuning Lightmass Settings
In your project open World Settings tab(you can do this from Windows menu). Seek for Lightmass settings section at World Settings and tune some of them:
Static Lighting Level Scale – use 1 or 0.75 to get the best result and 4 to get the fastest build time. But don’t change this value if you didn’t tried other options.
Num Indirect Lighting Bounces – the more is value, the more indirect lighting you will get. Usually I’m using value of 100.
Indirect Lighting Quality – To remove some lighting artifacts between meshes, try to use 4.
Indirect Lighting Smoothness – Try to decrease value to 0.75 to remove lighting artifacts between meshes.
Remember, this lighmap settings can dramatically increase light baking time. I recommend you to test your scene in preview or medium lightmap settings quality and when you will be happy with a result, set production quality for lightings. It will probably take a lot of time to bake everything, so be patient.
UV set for lightmaps.
You have to make a separate UV set for lightmaps in 3D modeling software.
All your UV borders should be snapped to the grid to prevent light bleeding. You have to setup your grid according to your lightmap resolution (try to start with 1/64 = 0.015625).
You have to get at least 2-4 px of padding between UV shells to remove seams and light bleeding.
Then you need to change lightmap size for your models in UE4. Start from 64 and try to increase values up to 1024. You can do it in mesh editor or by overriding lightmap resolution for certain models in your level. Use lightmap density viewmode to check if resolution is enough for your meshes. If you see green everywhere with a lowest possible values, then you set up everything correctly.
Set Screen Percentage to 200-300 in your Post Process Volume(in a Misc tab) to get better look for the whole scene.