I often run across Android layouts which use hard-coded margins, padding, and font sizes, like this:

Doing this often leads to inconsistency. Different layouts end up hard-coding different font sizes and margins, making the app appear less polished.

To avoid this, I recommend defining the sizes in values.xml like this:

And then referring to these sizes in your layouts like this:

If every layout uses only the sizes defined in values.xml, then not only will your app appear more consistent but it will also make it much easier to adjust sizes application-wide.