listen to some music that uses chords and scales predominently, even techno by the likes of UR or more specifically Los Hermanos, Galaxy To Galaxy where its more actual songwriting going on in places. Not wishing to state the obvious, but certain chords go together well, some dont, but they all follow a pattern in their respective keys. C, F and G are probably the 3 most common chords, with E, A and B after that. Then you have the minor keys, augmented keys, diminished keys etc etc. Really is a whole lot more complex than just playing it by ear, which does work, but if you want to right really solid, well written, well structured synth lines/chord patterns etc it really would do a world of good to get a good chunk of music theory, chord structures and scales learnt. Playing an instrument certainly helps, ive played guitar for 14 years so it all comes quite naturally now, but i remember first starting off thinking "WTF!!!!!!!!!", but now i could run through the whole scale of the chords in most keys including their minor, diminished, augmented 7th's etc etc, and im glad i can, as it brings a whole new dimension to producing.

check out some stuff by John Beltran too, he is a brilliant producer and has an amazing ear for melody and structure