A previous thread on construction kits got me thinking. Now don't get me wrong, everyone uses samples - unless you're some sort of hardware nut who does everything out of the box (believe me if I had the wonga, I'd have as many synths and drum machines as my studio could fit/the mrs would let me have) you're probably going to be using samples at some point.
Fundamentally in every tune I write, I use drum samples from a sample pack - single drum hits to build a kit which I then write a beat with. I might flesh those out with some sort of drum/percussion loop, which chances are you'll find in the same sample pack. Loops are a quick and easy way of adding depth and texture to your rhythm track because generally they've already been 'mixed' - perhaps some EQ, some compression and reverb - they sound finished. Start with the fader as low as it'll go, and bring it up slowly to sit the loop just underneath the drums you written.
Thereafter, it depends on what sort of producer you are. The basis of or inspiration for one of our tracks comes from either a great synth noise or melody, or a sample. For example the last track we wrote was based around a god-like rhodes riff taken from a live Jan Hammer recording. We used that as the central hook and inspiration, and wrote appropriate instrumentation around that from scratch using synths/pianos/strings etc.
However, I'd advise against sticking to working solely with construction kits - they are a great way for learning how your software works, and how certain generes of music are put together, but there's no creativity involved in re-constructing something that has already been constructed once. That's not to say you shouldn't pinch the odd sample from them here or there.
If you're finding writing melody lines difficult, you're not alone! It's really hard coming up with a killer riff. Try spending time working on a great sound, and remember the best electronic music (in my opinion) is painfully simple - some of the best 'dance' tunes ever are based around 1,2, or 3 note riffs. Pick one note, drop the software into record and have some drums to play along to, then play in a rhythm using that one note. After you have recorded the rhythm, loop up around that clip, then start playing around with note pitches until you get something you like the sound of. That's what I do!
Let me know what you think...