1) Export all tables that are in the affected tablespace
2) Drop any indexes in the affected tablespace.
3) Drop tablespace
4) Rebuild tablespace with the needed files
5) Import data exported in step 1
6) Rebuild indexes dropped in step 2.
First of all, good question and i understand you are undergoing your DBA training.
But, in real scenarios, the case always varies from environment to environment. So first you need to analyse your specific requirement as it is a easy job to drop/delete/truncate any thing in the database but difficult to get the same back.
Before dropping a datafile, you need to keep in mind, that by doing so no problem(s) arises.
The command to drop a datafile is as below:
alter database datafile 'file-name' offline drop; -- this command drops a particular datafile (for example, say file1.dbf located in '/u01/test/file1.dbf', then it is -- alter database datafile '/u01/test/file1.dbf' offline drop
Please see the following link. Please be aware that if there are any blocks in the datafile that are being used, you will cause file corruption and probably tablespace corruption. This clause is typically used on a totally empty tablespace.