Relativity makes a lot of sense and is absolutely correct! In reality, though, the question being asked is very, very hard to answer - in my opinion.
Why? Because any 'method' I or others may have depends on experience. You cannot shortcut this! So this is why I see it as a tough question.
So, to try and answer the question I cannot present a 'method', merely advice on how to acquire any skills necessary so that a method isn't needed. Everyone with me so far?
As advised elsewhere on the thread, noodle about as much as possible until you like the sound of things. There's no time pressure to record so just keep trying. But, in my experience, just hammering away at something and getting frustrated is counter-productive. I'd suggest an approach I've always used when learning/trying out new stuff:
Spend 5-10 minutes (a couple of times through a 3-minute tune) [i]really focussing[/i] on trying out what you want to play. If no joy, walk away, have a break and come back in 15 minutes time.
The brain, as a rule, cannot concentrate for more than around 15 minutes at a time. It is this time that you're at your most creative/focussed. After this time, your concentration and effort will wane until you're just wasting your own time and getting frustrated to boot. So work on a tune in 10-15-minute blocks of time with coffee breaks or whatever in between. I promise it will make a difference, if nothing else it'll reduce your frustration levels!
Secondly, going back to what I said at the start, it's about acquiring experience. As advised above, listen to lots of music and don't be afraid to nick licks and riffs and alter them. All music is a derivative of something that has probably been played before! But, as part of learning, listen to as wide a [i]variety[/i] of styles and learn their basic make-up. You may not like the style or music, but this is key to having a healthy musical 'palette'.
There's one reason I can jump on almost any track here and hopefully get the gist of it (ignoring any structural complexities). It's because I have a stock of 'basic styles' in my repertoire. If I hear a reggae track, I know straight away to start with the kick drum playing on the 2 and 4 or the 3 in half-time patterns. I also know staying away from the downbeat and playing fills that finsh either before or after the '1' is a signature of the style. If I hear a jazz track, I know to have hi-hat ticking on the 2 & 4 and quarter notes on the ride with a skip beat and fills generally contain phrasing or pushes. This may not be what I want to play, but it's my 'template' to work from - knowledge of the signatures of a style/genre... Furthermore, you'll be very surprised how you can completely change the flavour of a track by mixing these contexts. Take Ska, for example: that's just reggae and punk fused together!
In the guitar world I guess you could, using the examples above, start on a reggae track with a jangly guitar playing on the off-beat as that's the norm, or jazz you'd go for a nice round, clean tone with the top-end rolled off playing all those weird 7ths! Knowing these 'basics of style' really give you a springboard to jump in on a track leaving more time for you to enjoy it rather than worrying about it.
Lastly, learn the basics and learn them well. Rudiments (in the drum world) and scales/chords need to be learned along with basic styles as mentioned above. To me, without this basic knowledge and ability right there at your fingertips, you're just not painting with a full set of colours.
With experience, you'll be jumping on and off loops quickly and with fresh-feeling recordings.
Anyway, I'm rambling now (I've been writing for longer than 15 minutes!!!). I hope that helps in some way. Sorry for going on so long!!!