Bear in mind that if the helmet did its job most people would tell you that they did not even hit their head, or did not hit their head that hard. And the thin shells on most helmets now tend to hide any dents in the foam. But if you can see marks on the shell or measure any foam crush at all, replace the helmet.

The bottom line: Leaving your bike outside for a day or two won't do major damage. You may see signs of rust after a week of neglect. After one month in bad conditions, your beloved bike parts will start to degrade.

My 3 rules. 1.Be visible at all times. - Wear bright and visible clothes. Reflective stripes ads viability. Always stay out of blind zones. Alert other drivers before entering their blind zone.
2. Be predictable. - Others on the road must be able to predict your next move. Give proper signals before changing a lane or taking deviation.
3. Everyone in the road is dumb and partially blind. - Well, just imagine so and be prepared for an unexpected turn or braking.