Лучше бы я взял зонтик, тогда моя куртка не стала бы мокрой.

I really should have taken an umbrella; then my jacket would not have gotten wet.

Breakdown of Лучше бы я взял зонтик, тогда моя куртка не стала бы мокрой.

• я: I
• мой: my
• не: not
• взять: to take

Questions & Answers about Лучше бы я взял зонтик, тогда моя куртка не стала бы мокрой.

Why does Russian use лучше бы here? Is it the same as English should have?

Yes, лучше бы + past tense is a very common way to express regret about the past, often close to English I should have... or It would have been better if...

So:

Лучше бы я взял зонтик
= I should have taken an umbrella
literally more like
= It would have been better if I had taken an umbrella

A few important points:

• лучше by itself means better
• бы adds the hypothetical/regret meaning
• the verb usually appears in the past tense form

So even though взял looks like a simple past form, with лучше бы the whole phrase expresses an unreal past situation.

Why is бы used in this sentence, and why does it appear twice?