Always expect long data
When preparing layouts for MyDataMerge, you have to create placeholders. Please make sure that text frames which contain placeholders are big enough to provide enough room for even longer text replacements.
Move unneeded stuff to master pages
Instead of keeping all items on the regular pages, move everything that’s does not need to be merged (like decoration, background images…) to the master page. For large databases, this will speed up the process a lot.
Do not use styling options if every data record has the same styling
Apply styling in your layout document directly.
Use locally installed fonts
Adobe Fonts can be installed locally as well. When loading them online, this can massively slow down the merge process.
Scale images down
When merging thousands of data records its necessary to scale images down before the merge. No matter if the images are merged or part of the layout. This can save a lot of processing time.