The particular thing about a tile is that all images in a row are the same height. A tile can have several rows of different heights or of the same height – it totally depends on your personal liking!
To scale all images in a row to the same height, it’s a good idea to add some guides to mark the top and bottom of each row. Go to View > Rulers in the top menu bar and make sure that Rulers is ticked. Then you just need to click on the top ruler and ‘pull down’ a guide.
Now go to one image after the other and scale it to exactly the height you want all images to be in that specific row. Add as many rows as you need and scale the images accordingly.
When you make a tile in Photoshop, it looks better if all rows start and end at the same level. This can get a bit complicated because you need to choose the images for each row accordingly.
If you don’t want to do all the fiddling yourself, check out the Free Photoshop Tile Templates at the end of this post.
Last but not least, you can add some spacing between the pictures or a border around the entire tile – in whatever color that fits your artworks!