How to invoice and deal with production companies if you are a self-represented actor
Representing yourself obviously has advantages and disadvantages. Whether invoicing production companies is an advantage or disadvantage is down to personal choice. Some people like creating their own documents to keep track of everything and some people would rather it was done on their behalf. Either way, email is your key method of communication here, so make sure you've got a respectable email address - preferably just your name and nothing silly that you set up when you were 15. If you haven't got an email address you can get a simple free account from GMail.com or Outlook.com.
Most production companies generally seem to like dealing directly with actors, obviously there are exceptions to this, but it's a quicker more direct process than going through the agent who is busy and may take time to respond. Just make sure to check your email regularly! Then this continues into another point, production companies are busy organising a whole production. You don't need to repeatedly send them emails asking what's going on - there are lot of other things that need to be in place before an actor becomes top priority. If you agree to reply with your measurements or have a document signed and returned by a certain time then make sure you do. It's common courtesy and can only make you look unreliable if you repeatedly fail to deliver. However, a single actor, as opposed to an agent, may get a little bit neglected. It's not always deliberate, but it can happen, so just be aware that you might need to send a polite reminder if they said they'd contact you by a certain time etc. and don't take it personally, it's probably a slight oversight on their part.
The content and tone of your email depends on your relationship with the production company - you may never have met them before or you may be best friends. You'll be able to judge what kind of email you need to write, but it's advised to be friendly enough without turning it into a gossip, keep to the point, ask if you need anything clarifying and don't forget to attach any attachments if they're needed!
When it comes to sending invoices, first you need to create the invoice. There are various templates in Microsoft Word or Apple's Pages software so it's fine to use one of these and change it for your information. Alternatively, there are loads on the internet that you can download or copy the format of. The document should preferably be saved as a PDF document, this way it can't be edited by someone else. Also, save the document as something appropriate to keep their job simple - "invoice.pdf" could be anybody's invoice and could delay your payment if they can't figure out who to send it to. Go for something like "JohnSmith_Dec2012Invoice.pdf". Don't forget they need to know where to send the payment, a template will usually have an area at the bottom for you to put your bank details - account number and sort code. Keep a record of your invoice, save it in a dedicated folder on your computer and maybe even print it out.
Once you've made your invoice email it straight to them and politely request that someone drops you a reply email so that you know they've got it. Most companies will have a policy in place about how long it takes to pay you, probably 30 days. So now you get on with your life again, don't refresh your email every 5 minutes - remember they're busy people and they said 30 days. If it goes over 30 days then you could give them a nudge and send them a polite reminder - maybe around 32 days, but use your best judgement and don't forget weekends are business days!
Overall, be polite, be punctual and be easy to deal with. It's the little things, like correctly naming documents and making sure your phone number/email address are easily found, that make their job so much easier!