I also working in accounting....AP and Payroll Administrator plus have trained others in accounting software MAS 90/200/500. That software is really geared for big companies.....From the accounts payable (AP) point of view please be sure your invoices have an invoice number, detail of work done, a date on the invoice and where the work was done....plus the amount of course.

I like to know who, what, where, when and why. Who ... within the company I worked for, what ... was done for them, where .... was it done and why, when....when was the work done, that may not coinside with the date of your invoice. Most systems use the current date for your invoice date and if your invoice is dated Feb 1 but the work was most likely done in the previous month. Helps me to know how to code the invoice and what general ledger account I need to code it do. The more detail you can provide on any invoice, the better.
You may need to provide the company you are billing with a W9 also. Based on how you fill out the W9 for your company, corp, individual, etc. will determine if the company you are billing sends you a 1099 form at the end of each year with that same info going to the IRS. If your total yearly invoices for any company are under $600.00 then the company is not required to issue a 1099 but will most likely still require a W9 form from you. When 1099s are issued, most accounting software programs allow us to put a dollar amount for 1099s and won't print 1099s for any amount under $600.00.
I really love it when my vendors put their tax id info on their invoices not to mention if they are a corp, individual, etc.......saves me from having to contact them and getting a W9 from them. Plus allows me to process their invoices faster.
Also indicate when you want your invoice paid....net 10, net 30, due upon receipt, etc.....The net 10, net 20 and net 30, etc... are calculated from the date of your invoice and that is when you would expect payment....net 10 payment would be 10 days from the date of your invoice, etc.... If you don't indicate a due date, then standard practice is 30 days from the date of an invoice.
It is rare for a company to pay an invoice in a few days......there are steps that normally have to be done....the most time consuming can be sending an invoice within a company for approvals. Based on the company, more than one approval could be required.
Hope this helps some........