Not many artist work a piece at a time..."that one's finished, I'll have to think of another". That would be a recipe for disaster; any serious visual art must have a contextual thread which binds even seemingly disparate outcomes together. That continuous stream will surely mean that an artist's work, taking into account stylistic changes, will still engender a cohesive whole.
The most productive method, personally, is to have several works in various states of completion at any one time. Some come to fruition fairly rapidly, others linger around the studio in various states of completion...waiting for an infusion of additional imagery, ideas or research to kick them back into life. This period of hibernation can last for several years - mine tend to undergo this hiatus during the summer months; an inversion of the natural. I have dozens of sketchbooks, bags of clippings and cuttings, full of dormant notions and beginnings which have, at least as yet, not been developed.
For me it's quite often about patience; waiting for X then adding it to Y to create Z. The thing is that very often I don't know what X looks like... and I won't until I see it. Along the way I'll discard many x's, but when the right X is discovered it acts as the catalyst to galvanise the work. Lots of X's can appear at once (see above and below)...they may all appear in one piece of work but they can spark a number of works based around a similar theme or context.