How old is your toothbrush

Replace it if it's 6months old despite good shape
Replace it if it's 3months old and the bristles are flared
Replace it if you notice coloured deposits at the base
Replace it if the bristles are hard with a medium textured brush
Get a cover for it
Do not keep it in your toilet
Do not share your toothbrush with anyone
Avoid rigorous brushing to prevent trauma
Do a twice daily toothbrushing with fluoride containing toothpaste