Watch "465. Let's talk about my claws! Basic nail care." on YouTube
Start by eating right. Lots of fruits, veggies, proteins and water. Do not eliminate fat but eat a lessor amount. Make sure any fats in your diet include heart smart oils like olive oil or grapeseed oil.
Keep harshness away from your nails...chemicals, including nail polish remover can dry out your nails...so if you must use them, dont use them often and protect hands when you do. Only file nails every 2 weeks or longer with a course grit. Use a fine grit and a buffer for maintenance. File in one direction when you do cuz a sawing action equals week nails. When possible have your nails professionally maintained. An acrylic overcoat is fine...but more importantly, go for the manicure....it consists of someone spoiling you, soaking your hands in a moisturizing solution, pushing back your cuticles...more gently than you yourself would do, they clean under your nails, then they massage your hans all the way up to your elbow. Love that.
While at home, simple things make a big difference....check out the video for more on that. Above all else....keep your nails out of your mouth and the clippers out of your hands and you shouldn't have any weakened nails. Other than the risk of infection....nails to mouth and vise versa....nail biting is particularly bad for the nails becuz the same enzymes and such in your mouth that break down the foods you eat, wiill soften and weaken your nails. Keep them Squoval shaped....squared off oval. Look at your cuticles...thats the same shape. Rounded nails break much easier. Nails naturally grow into an oval shape, using the hands alot causes them to become rounded or point then they break....so square them off. Theres more strength in the square.
Challenge yourself...mark a calendar....and for 30 days....dont cut, bite, file or clip your nails. Make note of how much they grow in that time...if they break, etc. My nails grow about 1/4 in 2 weeks. Once I got them to the length i like, I file them every 2 weeks....sometimes 3. My general rule, I polish them and once the polish has a margin of about a 1/4 " of growth....time to do my nails. Be aware that skin, hair and nails show your health. If your nails aren't healthy, your hair has issues and your skin is erupting....the issue may be internal. If you are in good general health, these tips should work for you.
Hope this helps.