Legal contract terms and conditions for managed services

General information for the business: Marketing Agency
Industry: Food and Beverage
Legal topic: Contract
Description of legal work: I need to draft and finalise a buyers and sellers agreement for new clients I plan to sell a managed services marketing campaign package to. My team will be setting up and managing the campaign on behalf of clients across multiple sectors.

There are two types of campaigns we offer:

1. Fully branded - this is where our branding is not involved and we manage a fully branded campaign on behalf of a client. Campaigns can be either in the form of a social contest or a coupon offer.

2. Collaborated - this is where we partner with a client and we associated our branding with the clients and run a joint promotion, predominantly a contest where we mutually benefit commercially.

I'm not looking for anything too long winded and complex 2 pages is ideal one of which being the order form. I just want to legally cover myself with a few terms and to ensure I receive the payment agreed, even if a campaign is not as successful as anticipated.

We are a small start up and under a limited company.
Extra notes: I also have an additional mini project which is to update some Contest Rules (Scratch Card Contests) which at the moment the template is guided towards the US, I just want to guide it towards the UK and towards my particular contest model.