Account organization in Google AdWords should be aligned with your marketing strategy. Proper account organization is important to effectively manage your campaigns, budget, and targeted ads.
An AdWords account should represent an individual business. If you have multiple businesses or clients for which you manage AdWords account it is highly recommended that you create a separate accounts for each business or client.
A campaign represents a marketing initiative in a particular area within your business (e.g., sell more services vs. products). Campaigns allow you determine budget, language setting, geo-location targeting, etc. If you have different marketing budgets or you need to target your ads to different demographics, then based on these varying conditions you should create different campaigns.
Ad groups represent collection of keywords with a common theme. Ad groups can also contain different versions of the ads. For example, if you are selling different products such as LCD TVs and audio systems then you should create different ad groups.