The easiest way I have found to stay organized is to just take one day to prioritize everything. A good filing system is also a major help.
I'm not sure what type of business you have, but tweak away at what I do and build a system to suit your needs.
Incoming- When purchasing materials or products, set aside a place to put all of the quotes, purchase orders and packing slips for everything that comes in. When the invoice is either mailed or faxed, you can match it up (knowing you received everything and are being charged the price as quoted) and move it to the tray for things to be paid.
Outgoing- All of the invoices for things you shipped or work you have done, can be kept in one place and matched to checks or c/c payments as they come in. When the payment comes in, match it to the invoice and put it in the tray for deposits. Also payment descrepancies can be caught quickly and resolved with little to no issue.
Accounting processes can be done rather quickly on one set day per week. All incoming payments and deposits processed, then outgoing payments can be made. It goes really quickly and requires little time, since you aren't searching for everything, trying to match up paperwork or pricing.
Doing it on one day, lets you focus on the financial part, at one set time and everything else the rest of the week. The lines at the banks are long on Fridays and Mondays, so choose another day for it to minimize you time spent there.
For these first two things I use the expandable folders marked by the alphabet. Put everything inside by customer name. It's easy to go through once a month and check for old packing slips to be sure you recived the invoice or old invoices to be sure you received payment.
Quotes- Have another set of expandable folders for quotes you give. File all quotes during or at the end of the day by customer name. At the end of each month, put this file into the filing cabinet drawer. At the end of the year, quotes can be put into a regular folder and the expandables reused.
Purchase Orders- can be filed by month, by order number. This folder can also remain on your desk or close by and move to the cabinet at the end of the month. Ever have to go back and look? Knowing the month and order number, cuts wasted time drasticly if not out altogether.
Prioritizing, scheduling and having a place for everything will make it easy for things to run smoothly and you will get more accomplished. Good luck!