What should I monitor on the SQL Server machine? I need to create some alerts, logging jobs and monitors on a machine that is going to run SQL Server 2012 Standard for an ERP system. 

The OS will be Windows Server 2008 R2 Standard/Datacenter (if it matters).

I am planning to implement: server performance monitors (processor time, load, memory used, reads/writes to disk, disk space).

I don't know what should I be logging in terms of the database/SQL Server instance. I thought about autogrowth operations on the database and transaction log files. 
I guess I should be monitoring locks, transactions, connections and a few more things. But what exactly? Which activities should be logged only and which should be emailed to me ASAP?

I will greatly appreciate your advice as I'm a beginner in database administration.
Some of the options you mention (file auto grow for example) are already logged in the SQL Server default trace http://msdn.microsoft.com/en-us/library/ms175513.aspx

Other options for your own monitoring can be done via windows perfmon to monitor all kind of windows or SQL Server variables. You could also save output from any of the SQL Server DMV to store various options over time (query plan statistics, wait types, memory, locks etc).

You could investigate using the new Management Data Warehouse feature to collate lots of information http://msdn.microsoft.com/en-us/library/bb677306.aspx.

Having said all of that, that is going to be a steep learning curve and it is difficult to give a definitive answer. As a beginner is buying a third party tool that will do all this monitoring for you an option? Some packages are: -


http://www.sqlsentry.com/products/performance-advisor/sql-server-performance
http://www.red-gate.com/products/dba/sql-monitor/