If you have truly fragile nails there is unfortunately not much you can do about this, as it is often hereditary. Sometimes there is a role for nail strengthening lacquers, but they do not work as well as they are marketed to work.
The principle thing when trying to grow out your nails successfully is to avoid messing with them. Especially if you have a tendency toward fragile nails, you must avoid manipulating them in order for them to grow. This means you should not be trimming or clipping your cuticles or the skin under the nail. You should also avoid biting or picking at the nails, and you should be careful when performing work with your hands (wear gloves when performing household chores, for example).
Occasionally, a vitamin or nutritional deficiency or another medical problem (such as thyroid imbalances) can be associated with weak nails or nails that do not grow in properly. Therefore, if you have not had a regular checkup with your primary care doctor
in a while, you should do this. At the checkup you can mention the problems you are having with your nails to determine if there is an underlying medical reason, although this is unlikely.