To be in more detail below are the items you can monitor very specific to database...
Windows / Unix Oracle Service present for DB Instance
Windows/Unix TNS Service present for Listener
Can successfully connect to Database Instance
Suspended Sessions Exists
Datafile cannot extent
Autoextensible Datafile approaching defined maxsize
Rollback Segments with >50 extents
Processes approaching Processes Limit
Sessions approaching Session Limit
Recovery File Destination approaching defined maxsize
No corrupt data blocks exists
Blocking Sessions Exists
Excessive Waits
ASM Diskgroup usage approaching capacity
Check Segments can extend
Broken Public Database Links Exists
Alert Log contains ORA- Errors, incomplete checkpoint messages or archiver error messages
RMAN Resync has not run in last6 hours
Data Guard Health Check
No Data Guard Log shipping or applied gaps exists
No failed database jobs exist
Streams Health Check
Database files in backup mode
Flashback Health Checks
Check Segments can extend
Datafile and Redo Log Group limits
Segments with PCT_INCREASE >0
Sessions Highwater Mark approaching Session Limit
Invalid Objects exist
Nologging Objects exist
Statistics gathering failed or not gathered
Excessive Redo Log Switches
Orphaned Datapump Jobs Exists
Passwords expiring in next7 days
RMAN Backup log contains RMAN- errors
ASM and Database Alert Log, and Listener log sizes approaching1 Gb
Export Logs contains no errors
Default Users not disabled
