Cracks, sticky spots, pieces that pop apart, and wobbly shapes. Here are calm, practical things to check before you decide what to try next.
Before you try a fix
Is the clay still workable or already dry? Is the problem only on the surface, or does it go through the whole piece? Check your clay maker’s directions before adding water, glue, paint, or sealer.
My clay crumbles or cracks

Clay may dry at the edges if it is left uncovered or worked for a long time. Cover unused clay between steps. If your clay maker recommends it, add moisture sparingly and knead until the texture feels even. Avoid soaking it.
A small surface crack may be repairable only with a method approved for your clay. Deep cracks, crumbling, or a weak support are usually safer to remake, especially on an object that needs to stand or hold something.
It feels sticky and clings to everything
Let the clay rest briefly if the package allows. Use a clean, smooth work surface, clean hands and tools, and work with a smaller amount at a time. Avoid adding a lot of powder or water to force a quick fix.
The parts keep popping apart

Use the joining method recommended for your clay. A common method is to roughen both contact surfaces, add a little clay slip, press together, and blend the seam. Give the joint enough contact area instead of joining at one tiny point.
Check whether the clay maker recommends a compatible adhesive. Treat repaired load-bearing parts as untested. Remake anything that must support a phone or could damage another object if it falls.
The piece warped or curled

Uneven thickness, an unsupported shape, or uneven drying can contribute. Keep slabs as even as you can, dry them on a flat support, and avoid moving a piece while it is soft. Follow your brand’s guidance about turning projects. Do not use a heater, oven, or hot sun to speed drying unless the package explicitly permits it.
The outside is dry but the center is soft
Thick pieces can take longer to dry through. Give the project more time in a dry, ventilated indoor spot, following the clay maker’s guidance for thickness and drying. Wait until the whole piece is dry before painting or sealing.
Paint looks patchy or sealer stays tacky
Wait until the clay is fully dry, then follow the paint or sealer label, including its cure time. Thin paint coats can be easier to control than one heavy coat. Test finishes on a scrap if you have one.
When in doubt, remake with one change
Make the next version thicker, widen the base, simplify the join, or slow the drying. Changing one thing at a time makes it easier to see what helped.