Simply speaking… Do you mean I always put '요' at the end of each word or sentence to make it polite? Not always ^^; Let's see 잘 해(Good luck), 잘 해요, 잘 하세요. You know you cannot make 잘 해 into 잘 하세요 just by putting '요'.

'-(으)세요' is a verb＆honorific ending to ask something or order someone to do something politely. You can put '-세요' after getting rid of '다' of regular verbs.
Do 하다(basic form of the verb) ⇒ 하세요
Study 공부하다 ⇒ 공부하세요
Do you study Korean? 한국어 공부해?
Do you study Korean? 한국어 공부해요?
Do you study Korean? 한국어 공부하세요?

보다 see ⇒ 보세요　　보내다 send ⇒ 보내세요　　생각하다 think ⇒ 생각하세요

Let's turn back to 잘 해, 잘 해요, 잘 하세요(in this case, these stuff all means 'Good luck!') I'm gonna explain about 친구=friend(s). In Korea, if two people aren't the same age, they aren't consider to make friends with each other. I mean, the English word 'friend(s)' has a little difference from the Korean word '친구'. 친구 refers to friends the same age. You can say 잘 해 to 친구, and can say 잘 해요 or 잘 하세요(honorific style) to friends older than you.

When you learn Korean and use it, you need to consider 1) The listener's age, 2) The listener's style to treat people, 3) Something. People in their 30s and teenagers look at the world in different ways. I use the honorific to show my respect for people much older than me aside from some people are unable to act their age… ^^; About the second one, let's suppose I've just made friends with two girls they both are the same age, 7 years older than me. One says "말 편하게 해(means 'Don't use the honorific')" and the other one doesn't say anything. I would be able to get along with the first one very well because that kind of person is likely to be a bit more open-minded from my own experience. As for the 3th one, you can use the honorific when you talk with someone you don't want to get along with even if they aren't much older than you. It's why some people ask like "나 싫어하니? Do you hate me?" or "내가 불편해? Do you feel uncomfortable with me?"