Hey you might think that this advice is passing the buck but here is a few thoughts.
a)the Schoenbergian idea of total organicism is not really true unless you are writing serially or using pitch-class sets. However, having said that it is also true that the idea of development is often confused with variation. In fact in most cases development is a kind of non-obvious variation that takes place. For this you can look at Beethoven's Third symhony. b)In most cases development is the combination of variation techniques such as ornamentation or adding or leaving out notes with things like texture change and key change.c) Oh and remember that the most obvious kind of development technique is pattern and sequence or modified sequence. d)Another idea I have is that you can look at Mozart's structures. Ask yourself why is it that he sometimes repeats an idea and when does he change the idea - usually when the idea ends or is complete., he repeats or gives a modifeid repeat when the idea ends 'open'. Thus it has got to do with the level of closure that you find at the end of your theme and thus ultimately it has to do with the nature of your material or theme itself. d)Another idea that you can think of is that a theme does not necessarily give rise to the large-scale structure and that you need to impose one. Thus you might need additional material and work out a kind of narrative or if you want you can see that e) structure is a kind of psychological process that plays itself out as the music. Think for instance of the idea of a gradual process of change that takes place over a longer period of thime - this is very akin to the minimalist use of process-structure but you can see this also in the music of Ligeti. f)I think that you need to ask yourself first is if you want a clear sectional kind of form or a more fluid one.
g)oh and the last thing that comes to mind is that development and large scale form is a result of rythmic processes so that means if you have a good rhythmic grammar decided on it should give you an idea of how the form will be also hahaha!! Oh and remember that rondo form works very well for a lot of things and you can always modify the standard model to suit your needs).
lastly h) alwyas think about what you need for the piece and whatb kind of form will suit the character of what you are wanting to say -
hope this helps!!!