As everyone mentioned

1)backup and

2)you have access.

since you are asking for what are pref counters you need to look at.

since you have dba and dba is gone on vacation. so i am guessing that Your dba has already set up alerts for SQL environment.

Just make sure you don't serve same dish twice.

means If your dba already set up SQL alerts in environment just make sure you don't set up same SQL alert unknowingly again. which also impact on performance.

For performance tuning - since This is new for you . You don't need to jump on it unless There is critical issue. because performance tuning is ocean.

If i am new and don't have experience as dba i will start with backup & restore -security-SQL error logs- SQL jobs- SQL Server Configuration - database configuration -learn environment - Troubleshooting as issue occur -ask questions - start reading good blogs

Good luck.