1. Explain it simply
只有 introduces the ONE necessary condition; 才 introduces the result.
This means 'only if' - nothing else makes the result happen.
Put 才 after the subject, right before the verb: subject + 才 + verb.
只有 pairs with 才, never with 就.
2. Show examples
只有多休息，身体才会好。
Zhǐyǒu duō xiūxi, shēntǐ cái huì hǎo.
Only if you rest more will your body get well.
才 before the verb
只有多练习，才能学好中文。
Zhǐyǒu duō liànxí, cái néng xuéhǎo Zhōngwén.
Only if you practice more can you learn Chinese well.
只有 + condition
只有不下雨，我们才去。
Zhǐyǒu bù xiàyǔ, wǒmen cái qù.
Sandhi:Zhǐyǒu bú xiàyǔ, wǒmen cái qù.
Only if it doesn't rain will we go.
the only condition
3. Share a tip
只有 pairs with 才, not with 就. Keep 才 right before the verb (身体才会好), and use this only for the single condition that makes the result possible.