I put NO products on my nails. They will get stronger naturally. I have had mine grown out on my right hand for about 5 years now, and they are very very strong now.
Here are some tips for maintaining nails.
- Only have them as long as you need, the longer they are, the more fragile they become, and are more susceptible to being damaged from other things, like catching them on something.
-- TIP: A shorter nail allows more variety in tone, you can switch between using flesh, and using nail on the string.
- If you get a little bit of a cut in the side of one, FILE IT SMOOTH IMMEDIATELY. It WILL catch on something, most likely a shirt, and it WILL rip the end off.
- DO NOT CHEW YOUR NAILS
- Avoid using your nails for anything but playing ukulele. Try to avoid using them to open bags, and things like that. Picking your nose with them is fine however.
- Shape the nail so it is at the optimum pick angle for how you place your hand on the strings. For me this means slanting them off to the right (If looking at the back of my right hand)
- Avoid using nail cutters to shape them. Because of the way nail trimmers apply pressure across the nail, they can weaken it by flexing it in directions it doesn't want to go. Use a really gritty file to get rid of most of it.
- Remember to use a fine file on the top and bottom nail edges, and remember to get the UNDERSIDE of the nail, that's the part that makes contact with the string. If you remember to round the edges with a fine file, the nails will be less prone catching on things or tearing.
Tapping your nails is said to strengthen them as well.
EDIT: You can see in the photo how I have them trimmed for my optimum picking angle, with the exception of the index finger, as I use that like a normal pick often. If you were to trim them normally, the nail edge would slide along the string. But because they are slanted, they are more of a parallel contact on the string, creating a more aggressive pick. Making some form of a point will also help with the attack. If you leave the sides of your nail square, they are also likely to tear more often, and it makes picking the instrument more difficult.