what is the best practice for tempdb autogrowth?

For me, the best practice is to just size the files large enough, at the outset, to accommodate the growths you expect.

Let's use some simple numbers. Say you have a 100 GB drive that you've allocated to tempdb (or 100 GB of some shared drive). Your instance has 4 tempdb files, and you've decided to set them initially at 100 MB and to grow 10 MB at a time. Initially, that 100 GB drive or slice looks like this (not to scale, obviously):

As your system uses tempdb resources, each tempdb file will grow, 10 MB by agonizing 10 MB. After a few growths:

Note that each growth event, while likely fast-ish, forces all connections to wait. This is more pronounced when Instant File Initialization is not enabled, and if the files are configured to grow together (which requires a trace flag in some versions, but this is the right thing to do, because you don't want any single file to be bigger than the others).

When you get to the end of the drive, all 4 files will fail to grow at the same time. And this is a business continuity event. When tempdb can't grow here, activity halts:

Now, if you're getting to this point, ever, you need to acknowledge that either you need to change the way you use tempdb, or 100 GB isn't enough and you need to allocate more space. But I would argue that it's better to simply start here and configure this size for your tempdb initial data file sizes:

Well, technically, I would size them at, say, 20 GB each, with a 500 MB autogrowth. This allows you to still be warned well in advance of filling up the 100GB slice, but without paying for all of those incremental file growths in the meantime.

After all, if tempdb is going to grow to fill that space, it's not like you can use it for anything else.

which size should i give the autogrowth

There is no magic number (the defaults have been traditionally way too conservative for practical use, but this is getting better). Your autogrowth setting will be based on the performance characteristics of your disk, and how often you expect to grow. If you have SSD or similar, and have IFI enabled, size is probably much more tied to how much warning you want to have before hitting the end of the slice. If you have spinny, mechanical drives, and/or don't have IFI enabled, you will probably want to test various settings and see where the time it takes to grow the file by different amounts meets your tolerance for all transactions on the system to wait.