if an oracle datafile gets too big for the directory what does one do

if an oracle datafile gets too big for the directory what does one do

if I have a datafile in a directory and it is getting too big for the
directory what command in Oracle can I use to move that file, or do I make
another datafile into another directory?
ALTER TABLESPACE
users
ADD DATAFILE
'/ora01/oracle/oradata/booktst_users_02.dbf'
size 100m