Make observations but don't try to be an arbiter: Say "This function is long." but don't say "This function is too long." You can soften that language by using

Make observations but don't try to be an arbiter: Say "This function is long." but don't say "This function is too long." You can soften that language by using phrasing like: "This function has grown long." Explaining how to resolve a problem if the solution is obvious can be perceived as rude. Avoid. Don't tell other programmers how they have to solve a problem either - it's their job to figure that out - make suggestions instead. If you want to make a suggestion, explain how it addresses the problem and if possible put an emphasis on improving things for the sake of others: "Extracting this to a separate function would make it easier to grasp." Brief, helpful, and you're not appearing like you want to hold anyone's hand or micromanage them.