You should put water on your toothbrush before toothpaste.
Putting water on your toothbrush before adding the toothpaste to the toothbrush will help the toothpaste adhere better to the toothbrush.
Wetting the toothbrush with water before adding the toothpaste also helps soften the bristles and helps the toothpaste spread.
You should replace your toothbrush as often as every 3 months to 4 months.
Or if the bristles of the toothbrush become frayed, splayed or worn out then it's time to replace your toothbrush.
Also if you've been sick and used your toothbrush when you've had strep throat, flu or cold or other illness, then you should also replace your toothbrush to prevent reinfection.
Or when toothpaste or stains build up at the base of the toothbrush bristles or when the toothbrush bristles start to bend outward then it's time to replace the toothbrush.
The most common sign that your toothbrush is no longer effective at cleaning your teeth is the bristles being splayed or frayed and so the toothbrush needs replaced.
Also never share toothbrushes with others and rinse the toothbrush off after each use under some water.
Then shake any excess water out and allow the toothbrush to dry.
Keep your toothbrushes away from others so that someone else doesn't accidentally use your own toothbrush and get sick or contaminate your toothbrush.
I replace my toothbrush every 3 months regardless of how good it looks as they are cheap enough to just replace and I also keep more toothbrushes on hand to replace them easily.