In terms of menu structure, users expect to see either a horizontal menu across the top of the website (possibly with drop-down boxes to integrate sub-menus) or a vertical menu running down the left hand side of the page. Never use a menu on the right hand side of your website as the right hand side tends to be associated with advertising or secondary content. If you have something important to convey, make sure it is placed in a position to where the eye is naturally drawn. Long menu items such as 'Search Engine Optimisation Cardiff' may be better in a shorter form, such as 'SEO Wales'.
Drop-down menus can be a fantastic way of organising content but you will need to ensure that your SEO plan is adhered to. Don't use menu forms which aren't accessible for search engine spiders. Using a simple HTML and CSS drop-down menu will ensure that search engines are able to reach all of the pages on your website and index the information they find there. Without this, the pages won't be included in the search engine's index and you are unlikely to rank very highly for any of your search terms.
If you need a hand with any aspect of your Website Design Cardiff, Wales or the rest of the UK, please do give us a call. We also specialise in SEO Wales and all over the UK so can offer many good words of advice to help your website rank higher in the search engines.