We don’t usewillandwouldin the conditional clause:
If youbookbefore April 30th, you will receive a 20% discount.
Not:If you will book before April 30th, you will receive a 20% discount.
If wehada bigger flat, we could invite friends to come and stay.
Not:If we would have a bigger flat, we could invite friends to come and stay.
If the weatherhadn’t beenso bad, I could have gone to meet them.
Not:If the weather would not have been so bad, I could have gone to meet them.
We don’t useshallorwillin the main clausein second conditional sentences:
If you worked harder, youwouldearn more money.
Not: …you will earn more money.
Wedon’t useunlessandiftogether:
I’ll try to get there about 6.30unlessyou want me to arrive earlier.
Not:I’ll try to get there about 6.30 unless if you want me to arrive earlier.