Nothing much. Unless you're taking certain meds that can slow the hr, nothing you can do to increase your resting hr. There are a few potential causes for sinus bradycardia but make sure you don't have something else such as heart block. Assuming you were hospitalized because of symptomatic bradycardia (slow hr), you need further eval. And f/u with a cardiologist and possibly an electrophysiologist. Good luck.
Check meds. If there is truly a problem with an abnormally slow heart rate, then there is little that the patient can do. One of the most common causes of slow heart rate is medications, and your doctors should review any meds (or supplements) to see that this is not the problem. Heart rate slow enough to cause fainting or other major symptoms may require treatment with a pacemaker.
Watch for symptoms.. Sometimes theophylline might help but may cause other problems eg. Anxiety. Diagnosis of the cause of low heart is the first step to treatment. Thyroid function may also need to be evaluated. Holter may be useful. Need to see cardiologist / electrophysiologist.