How to remove or decrease the tile effect caused by vision distance in Terrain or Objects.
See the grass material from starter content. It should give you an idea how to decrease tiling on landscape.
What i like to do with tiling images is offset the already tiling image by half image size both in x and y in something like photoshop. So that the edges become the middle of the image. It will reduce the amount your eye will catch the edges of the tiling, but be warned if you do this it might ruin your tiling image and you might have to fix it and some tiling images might look worse.
Just add some variation in your material -> e.g with a macro and micro variatin texture or another dirt texture that is randomly blended into the original texture (as Shantaram mentioned, you can find something like that in the grass material from the starter content)