craigb
Turn on some type of recording device (even a phone works) then play whatever you want on a piano (along with random stuff). Go back and listen to the recording and see if there are any "Ooo... THAT has potential!" parts then flesh a few of those out. The key is to not think about it during the recording process, just let things flow and completely ignore anything that doesn't sound good! 
Yeah done that before only right now the melodies sorta come easy to me. The only thing I'm thinking about is that if they come that easy, they're probably no good and I'm fining it hard to decide what to use.
jamesg1213
Here's a couple that might give you some inspiration;
Good choices. thanks.
sharke
The Lark Ascending is a good one, loads of great melodies in there. In fact Vaughan Williams' stuff is a treasure trove of amazing melodies, some of them taken from English folk music.
To me one mark of a good melody is its whistleability. The first melody in "English Folk Song Suite" by Vaughan Williams is a fine example. It has every good hallmark of a great melody and I whistle it all the time. Another great trove of melodies is Holst's "Jupiter" from The Planets.
And you can't discuss melody without mentioning Mussorgsky's "Pictures At An Exhibition."
I think good melodies have a pleasing element of symmetry in them, and they might also have a linguistic element to them as well.
Thanks for the suggestion. Jupiter is a perfect example of what I'm looking for. Very beautiful ! Not too familiar with the british composers.