Can you give a number of examples? I can't comment on what you say without knowing what you are referring to.
I don't remember all of them but, in Mark 11:1, he says that Jesus traveled from Jericho to Jerusalem by way of Bethpage and Bethany, when in fact, Bethany was between Jericho and Bethpage. Matthew does not repeat this mistake.
Then, in Mark 11:10, he quotes Jesus as saying "Blessed [be] the kingdom of our father David." However David was not a patriarch. Jews would never speak of "our father David." Matthew omits this line.
I also seem to remember reading something about Mark placing the beginning of Passover on the wrong day but Matthew getting it right.