This is a very open ended subject. There are a LOT of different reasons that this can happen, and we are going to try to cover the most basic ones here.
1: My leaf tips turned brown almost overnight it seems. The browning stopped at the tips, at half the leaf, etc.
You my friend overfertilized your clivia. Clivia do not require a ton of fertilizer. Check out our "how to grow clivia" section for our fertilization techniques. This happens to everyone at least once. Heck it happens to us when we try to push blooms sometimes!
2: My leaf tips turned this wierd bright yellow/orange color and then turned brown. This slowly has been continuing down the leaf.
This can be a sign of malnutrition in your plant. What you need to find is a good trace element supplement to your current watering regime. Most good fertilizers have a decent amount of trace elements for a clivia in them already but sometimes you just plain miss one. It can even be due to how a plant has been handled to be shipped to you! Many overseas sellers will use flowers of sulfur to prevent disease when shipping a plant. Although plants "eat" sulfate, they cannot convert sulfur directly to sulfate themselves. A supplement like Cal-Mag will take care of this and most other deficiencies (Iron, Calcium) for you. Epsom salts supposedly can also be used in the case of the sulfer issue but we have not personally done so.
3: My Leaf tips turned brown and crinkly and the leaves have brown spots on them as well (not raised bumps, brown spots)
This is a fungal infection. Choice A and B in the first section of "My plants have problems" can be used to help with this. We also reccomend repotting the plant. I know it sounds weird but sometimes this is caused by root issues.
Alternatively, and unfortunately, your poor plant may have contacted a Viral Infection.
Viral Infections are not really curable just as they have to run their couse same as humans (ie: common cold).
Some plants can co-exist with a Virus for years and others succumb fairly rapidl;y.
Everyone who has ever kept plants has had to make the difficult decision-keep the plant and cut virus laden parts off or dump the plant for the greater good.
Personally, I have not found "saving" virus laden plants to be particularly beneficial to the plant group in general. Even thjough I have set up many "hospital wards" I believe in the end 99% of the plants eventually had to be destroyed.
It's your choice.
If you can not ascertain what is hurting your plant, youi can always bring it to a lab or County Extention Center.
4: Overnight my leaf tips turned a black color and curled up, my plants are indoors.
Move your plants away from your space heaters. Cut back the leaves that were effected.
5: Overnight my leaf tips turned a black color, my plants are outdoors.
It got too cold, your leaves just got hit by frost. cut them back.
We wish we could say this is every issue that can blacken or brown a leaf tip, but it isnt. Hopefully this guide helped you!