How did people get to heaven before Jesus was on earth?

People didn't go to Heaven before Christ came to Earth and died. Right after his death, the curtain in the temple ripped in 2 (Mark 15:37-38), symbolizing the way to Heaven was now open. (Hebrews 10:19-20) Worth pointing out too, is that not all good people go to Heaven. A specific number (144,000) are handpicked by Jehovah God and Jesus to go. (Revelation 14:1-4)

So what happens to all the other good people that have died but didn't go to Heaven? These (along with those that died before knowing anything about Jehovah or His principles, a.k.a. "the unrighteous") will be brought back to life in the future. (John 5:28-29; Acts 24:15) These individuals will then be able to live forever on Earth in peace, in a world devoid of evil people. (Psalms 37:10, 11, 28-29)

(New World Translation of the Holy Scriptures)