Adjusting your site to help it appear more organised to players and more searchable by the search engines will give you the edge needed to make it stand out. Initially, the best way to make sure your site is going to be good for the players experience is to get a friend or family member to go to the site and try and play a game. If this causes them an issue then you are going to find that real visitors to your site will not attempt to try and work it, but instead go on to another site. This is one of the first rules, it must be quick, easy to navigate and simple to use.
Speaking of navigation, making sure that it is easy to find your way around the site is also important. Is there a search field on the home page. Can you browse to the game you want to play easily? Are there related games that may be of interest to players when they have completed a game? The main reason for all of these tasks is to keep people on the site and playing other games. What about if a player enjoys a game, can they tell friends about it or rate the game? Never under estimate the power of word of mouth marketing. It is the best type of marketing going! Think about having a plug to Facebook or Twitter. Maybe even get the option to log in with a Facebook profile when joining the site to make registration easy to do.
Organising games in to genres will keep things in order and all types of games together. Keeping all kids games together, classic arcade games and puzzles all separate will help make the site organised and help the search engines send search results to the relevant pages and categories.
Finally, the main promotion is to tell people about your site, but you only want to tell people who are interested in the online flash games community about a site relating your arcade games. Therefore it is recommended to submit your site to a flash games directory and this will reach out to the relevant types of people and hopefully drive visitors to your site. Keep your entries in the directories relevant to your topic and only link to the relevant pages. There is no point linking a puzzle game to an arcade game based category. Tell the right people and you will see more activity on your games.