Use would when you're imagining something unreal or unlikely right now or in the future. If your sentence says If I had more time, I would call her, you're saying you don't have that time, so would fits the imagined result.
Your situation changes the wording
Imagining right now: when the situation isn't real, put would in the result. If I had more money, I would buy a car. You're saying you don't have the money, so the buying stays imagined.
Something unlikely in the future: use wouldn't when the imagined result is negative. I wouldn't go to the moon even if I could; it's too dangerous. The trip isn't happening, and you're saying why.
Thinking about next week, not today: the form doesn't change, only the time frame you mention. If I had money next week, I would spend it on a trip. Same pattern, just aimed at a future moment.
Regretting the past: switch to would have with a past participle. If I had studied, I would have passed the exam. Here the studying didn't happen, and would have marks the result that never arrived.
Likelihood is the deciding line
The qualifier that flips your choice is how likely you think the condition is. When you're picturing something that could actually happen, will sounds honest: If it rains tomorrow, I will stay home. You genuinely expect rain might come.
Swap in would and you've quietly told your listener you don't believe it: If it rained tomorrow, I would stay home signals the rain feels imaginary to you. Same sentence, different likelihood, different verb.
Do you expect the condition to be real? Keep will in the result clause: If it rains tomorrow, I will stay home. The rain could genuinely show up.
Would you bet against the condition? Put would in the result clause: If it rained tomorrow, I would stay home. You're telling your listener the rain feels imaginary, so the staying home never gets tested against reality.
So when you draft the sentence, ask yourself one question: do I expect this condition to be real? Your answer picks the verb for you.