Think of objects that visually resemble spikes to associate with 'spiky' - like a hedgehog or a cactus. The little hedgehog had such spiky quills, it looked like a pincushion!
Pro Tip 2/3
Physical Sensation
Imagine how it feels to touch something 'spiky' - careful not to prick your fingers! He didn't dare to grab the spiky sea urchin with his bare hands.
Pro Tip 3/3
Not Always Negative
'Spiky' can describe something positive, like funky hairstyles, not just dangerous things. Her spiky hair made her stand out in the crowd.