There are two kinds of hair clip and mixing them up is why people's hair falls down. One kind is structural. The other kind is jewellery that happens to be shaped like a clip. Both are good. They are not interchangeable.
Butterflies hold nothing
A butterfly clip holds a small twist of hair and its own weight. That's it, and it's fine — they're decoration. If you're relying on them to keep an actual style up, it will come down, and you'll conclude the clips are bad when they were simply never doing that job.
Use claw clips or pins for the structure and scatter butterflies over the top for the look. That's how it worked the first time round too.
Clean hair is the enemy
Clips grip texture. Freshly washed hair is smooth, slippery and conditioned, which is the worst possible surface for anything mechanical. Second-day hair holds clips effortlessly, and if you need it today, a small amount of texture spray at the roots does the same job.
For snap clips specifically: fold a twist of hair under before you close it. Clamping a flat sheet of hair means the only thing holding it is friction, and friction loses.
Odd numbers, uneven placement
Two clips read as an accident. Symmetrical clips read as a school uniform. Odd numbers, deliberately uneven between the two sides, reads as styled — and it's a strange rule that works consistently.
Also worth knowing: the very small ones snag coming out of fine hair. Open them properly rather than pulling, or you'll lose more hair to your accessories than to your hairbrush.
Structure from claws and pins, decoration from butterflies, second-day hair, odd numbers.