Oracle Database Discussions

Hi All,
I need to refresh one of my development database using exp/imp utility,i did refreshing using the copy datafiles but new to this ,i have gone thru this forum and did some search on google too but the part that am not getting is suppose my development db already created with same tablespaces name and size and containes every schema as that of source and has data in it which is refreshed earlier, so do i need to wipe out everything and do it right from scratch(create db,tablespace,users) or just wipe out tables and import with (ignore=Y) .Any feedback would be apperciated.

Thanks