"If" for beginning conditional clauses is *pi.
Place it at the beginning of the phrase that it is subordinating. We don't know if it would cause mutation or not, so that is up to you.
*Cí means "maybe" or "perhaps". Again, we don't know if mutation should follow it or not.
*Pi le beren maethathol. - If you are brave, you will agree to fight.
*Cí dolathon ab in yrch dengin. - Perhaps I will come, after the orcs are slain.
Another word used for "if" is *ae, created by David Salo. It was made popular by the movies, so many people prefer it.