After, no trick, I start at the top IF I use garland. I just use “filler” now , not sure of the correct term.

I don't always add a garland but have done it both before and after the ornaments. Depending on the type of garland, doing it before the ornaments can mean less rearranging of ornaments. I've used garlands that are just a thin wire covered in gold or silver with tiny stars. Those I tend to spiral around the tree after the ornaments. Parts of the wire don't even touch the tree making the garland appear as if it's almost "floating" around the tree...if that makes sense.

I do my ribbon like this so it is added after all the decorations but just before the topper

When I used to use garland, I found if you put it last, it becomes the focal point and some small ornaments couldn't be seen. . So I liked putting it after the lights and before the ornaments as ninigret said. That way the ornaments are more the focal point.

and i'm going to agree with patricia that ribbon is different than garland and should be done last... like the ribbon on a package!