In Genesis the most often verses used to try to "prove" the trinity are the fact that Elohim is plural, and the verse that says "Let US make man in OUR image" and the story of the 3 angels of "the LORD" that visit Abraham. All of these are an attempt to say Jesus was there with God from the very beginning and interacting with the fathers and prophets. But we can see from Hebrews 1 that this isn't the case at all.
Hebrews 1:1 God, who at sundry times and in divers manners spake in time past unto the fathers by the prophets, 2 Hath in these last days spoken unto us by His son, whom He hath appointed heir of all things, by whom also He made the ages (aiōnas)
Hebrews specifically tells us that God was not speaking through His son Jesus until "these last days". When God spoke to the fathers (in the time of the Old Testament) He used prophets to speak to them.
The bible interprets itself, to see how God made people in His image (singular) but also made us in "our image" (plural) and why even though the word Elohim is plural it doesn't mean God is plural, click here: Genesis 1:1 & Genesis 1:26.
Some trinitarians will use these verses to say that since these are "men" and Abraham bowed down and called them "My Lord" that they must be the trinity, or at least one of the men must be Jesus, because Abraham was still standing "before the LORD" while "the LORD" rained fire out of heaven. To see what was really going on, click here: Genesis 18-19.
Some trinitarians will use this verse to say YHWH provided the lamb and the lamb was "himself" to "prove" YHWH was the lamb of God, Jesus. But we know according to the story of Abraham, that God provided a ram to Abraham. Trinitarians ignore that YHWH was not the ram that Abraham sacrificed. To see what's really going on in this passage, click here: Genesis 22:8