Producing a Finished Work

Whilst starting a work can be difficult, finishing can be equally tricky, demanding a level of awareness that can often leave a budding artist flummoxed! Often knowing when and how to finish a work sets an inexperienced artist apart from an experienced one.
Problems Surrounding Finishing an Artwork
There are principally two main mistakes when approaching finishing an artwork - finishing too soon and not knowing when finishing would be a good thing. In the first case an artist will be over content with their result and fearful of pushing through with their work to a stage beyond what comes most easily. In the latter case the artist will not realise when they are on to a good thing and will push the artwork too far, erasing the traces of the original picture and overworking it so as to ruin it.In both cases it is a good idea to have a clear objective in mind and to work to fulfil that objective. Certainly, chance can play a part within an artwork, but it is best practice to have a clear intention of the outcome you want, so that you can work to that point and no further.
Returning to a Work
When you have gained in experience and become more ambitious you might consider reworking some of your old 'finished' pieces. This seems to go against the advice given, but it is true that the benefit of hindsight allows changes to be made over time, as with the case of Picasso's groundbreaking Les Demoiselles d'Avignon, which was reworked over a few months. This only works insofar as you still employ constant revisions to achieve a certain effect, and not blindly for the sake of it.Often these revisions will be apparent in the finished work and will contribute to the feel as a sort of 'labouring' effect. However, one would need to engage in this kind of reworking of a work over time knowingly and with intent, rather than haphazardly!
Going over and over a drawing, for example, may enable the artist to avoid the pitfall of leaving the work in its early stages, before it is really ready to be termed as a finished piece. It may however, result in the work being over managed, resulting in a brown mess of paint or a grey fog of a drawing that is beyond redeeming. That is why experience is the best assurance that work can be finished appropriately and to a reasonable standard.