What's up with you trying to reword the previous persons post every time? You've posted 3 times in this thread as if you're trying to take it over and show off your misspelled and confused terminology. Making sure the tune doesn't have mixed emotions isn't good advice, what if that was the point? That could be the thing that actually makes your tune catchy if you did it in a certain way. I know you like whipping out the circle of fifths, but that's basic stuff and once is enough.
If you have to refer to the circle of fifths to write a melody then there's other things you could be doing instead of trying to create catchy melodies. My advice is get a good idea in your head of what you think sounds good. Listen to the stuff that you like and then compare it to your melodies. Your music will come out sounding like you want it to sound if you know how to form it that way, and part of that process is blocking out the crap stuff. So as soon as you write a few notes that don't work - cut them out and go back a step instead of continuing. If you do this, your music will come out as you let it.
Pay close attention to tune development, and like I said before, HOW it interacts with the chord progression. The guy above me tried to reword my post but completely misunderstood what I said. It's got nothing to do with picking out chords in the "circle of fifths" it's about how you treat the whole process with these chords. For example, you have a progression in mind - do you need to bring it all out at once? How can the tune relate to the chord changing? A good example is the 6th chord. Because this is a minor chord of the major key, (for example, in C major, chord 6 is Aminor)
this can evoke some sort of emotion with the right melody. So let's say you are playing around with chords I IV and V in some way. Or maybe just two of them, or even just one chord. Then you introduce chord VI - the Aminor (if we are in Cmajor). The melody could go up here. Or it could go down in such a way that it evokes an emotion. Hold back, use restraint. When this chord comes in, the feel changes. How can the melody work with this? Do I have to use a million notes here? Will only one note work? These are just a few of the things you should be thinking.
Tune development should be a natural, honest process. Forget your theory book. Study theory, yes, but not at the same time as you are composing. When you are writing, use the theory you have, chuck it in the back of your brain and then whip it out with restraint.
Some people like to sound mature by using lots of words to impress. But the real maturity lies in the restraint that true smart people know how to use. And it shows. Same sort of thing applies with music. Don't show off, nobody but University or classical wanks will care if you change key signatures every 3 bars. But people will know if it sounds like rubbish because there are a million notes and no melody.
The melody going up and down in certain places evokes different feelings and with the right restraint can be amazingly powerful AND catchy at the same time. Some of the worlds catchiest (and most annoying :P) tunes are just over two chords and just repeat forever, and then some are more complex, both are equal in their own rights.
While this advice is one way to go about it, the best way is to just listen. Listen to your favourite music and play it. Don't just give it the once over general listen - find out why it's good! And then you'll know everything you need to know to make your stuff sound just as good.
Keep composing, do it all the time, every day. Whenever you can. The more you do, the better you will get. And you won't notice it straight away, but I swear, compare your stuff months apart, or a year, and you will notice big differences. And by the time you are ready to write "catchy" tunes, you won't need to ask how, because you'll be ready to do it yourself.
Chris