Deciding what kind of scheme you want to establish will be the first and most important decision. Will the scheme offer 'defined benefits' (often called a final salary scheme)? In this kind of scheme, the pension benefits are worked out by a formula - usually factoring in the member's salary near retirement and the length of time that the member has contributed to the scheme. The member usually pays a fixed amount, with the company contributing more or less, depending on how the scheme's investments perform and on salary growth.
Alternatively, will the scheme offer 'defined contribution' benefits (a money purchase scheme)? In this kind of scheme, both the member and the company contribute fixed amounts, and the amount of pension available depends on how the 'pot' invested for the member grows over the years, and also on how much pension the final pot will secure from an insurance company at retirement.
Will the scheme satisfy the stakeholder pension requirements? Will it be trust-based (an occupational scheme) or will it be a personal pension scheme, where each employee has his or her own portable insurance policy? If it is to have trustees, then what scheme administration powers will they have as against those of the company - eg who will have to approve early retirement benefit requests? You will have to consider how the design fits your staff's needs (and how it fits with your commercial obligations - eg if you have taken over a business on terms that a new scheme will be provided) and, of course, you will have to consider what it is all going to cost.
You will have to take your chosen benefit design through all stages of scheme implementation. Consequently, it is important to speak to the legal advisers early in the design process. That way, you will have a feel for the extent and complexity of the legal work needed to put your proposals into effect. Are you going to be able to communicate a complex design effectively to your staff, for example? What is it going to cost to put the formal 'governing' documents into place?