Is there a "sweet spot" for you when it comes to invoicing?
My sweet spot for invoicing? It's really a week to 30 days before the job, when we send an estimate and agree on a budget.
The two tips that have worked bet for my business (Check out Getting paid: 2 surefire ways), have been getting a 50% deposit or retainer, before starting work and secondly being able to show a client my finished product (images and video) digitally online. High re photos or final edits can be viewed, but not used on their websites, catalogs, etc.
Once final payment is received, i.E. on delivery, images and video can be downloaded with a click of a mouse.
If you want to read the article I mentioned in this post, please go to my blog (the link is on my profile page) and type "Getting paid: 2 surefire ways" into the search field.