Bonsoir,
La forme à utiliser est : if + subjonctif, would+base verbale,
où le subjonctif est identique au prétérit, sauf pour "to be" où c'est "were" à toutes les personnes.
1) If he started, he would finish in time.
2) If you worked harder, you would do well on the test.
3) If I were you, I would accept the offer.
Rq : On entend souvent "If I was you", ce qui est techniquement une erreur mais passe à l'oral.
4) If she knew who he was, she would not love him.
5) If I were you, I wouldn't do it.
Rq : De même, on entend souvent "If I was you".
