Twitter and Facebook are the giants of social media networking platforms. There is a lot of opportunity to promote your company on there and you do not necessarily have to spend money in order to do it (although obviously that helps!)
In order to promote your business effectively you need to know what to do and more importantly what not to do!
A big problem with a lot of people who use social media (or who maintain accounts on behalf of companies) is that they focus almost exclusively on the product or service. There is nothing wrong with being passionate about your product or service but if people only see endless posts linking to your website and only talking about it then they are unlikely to follow you.
This means posting about other things. For example if there is a big local event on then talk about it. Linking yourself to a local sports team or a networking group is a good way of linking yourself with likeminded people and this can often make it easier to market to them.
While you don't want to focus solely on business it is also a bad idea to only focus on the trivial and the irrelevant as well. You want to show that you are having fun on the site but you need to remember that (like it or not) you will often be the face of the company and what you say will be representative of others (Putting "My views are my own" is a cheap get out and most people are likely to ignore it, especially if you're the boss!)
You also need to be wary of discussing anything overly controversial, especially politics or religion. Again saying that people shouldn't engage if they are easily offended is not an acceptable get out clause. Take responsibility for what you say!
On Facebook groups are a great way to talk with people who share interests. Be careful though as you need to avoid spamming. This means sticking to one promotional post a day, contributing to group discussions and generally being a good online citizen.
Hashtags on Twitter are a useful shorthand and an effective way to bring people to you. #FollowFriday is the most well known. The idea with this is not to promote yourself- a post or two is OK but it is mainly about encouraging people to follow your other followers. This "pay it forward" attitude often pays dividends, with others often encouraged by your efforts to help them!
It seems like a no-brainer pay a celebrity to endorse your product or service on Twitter. Unfortunately in reality some celebrities have been criticised for not openly declaring endorsement deals (and in some cases have been fined).
It is better to take a more subtle approach- if you have a charity event coming up a celebrity is more likely to endorse it. Also don't be cynical- follow them because you like them, not because they have a lot of followers!
Marketing via social media takes time. Fortunately Facebook pages have graphs and statistics that make it easier to measure your campaign. Remember that quality is just as important as quantity- you want a number of people following you who are willing to spread the word and will promote you because they like you (although throwing in a few special offers does help!)
If you are a big company or you are looking to develop a long term strategy you are probably considering using the services of a marketing consultant, a virtual PA or other service to help run your social media and generally make life easier for you.
How many people are following them? Do they follow their own advice?
How experienced are they? Do they seem like they know what they're talking about?
Do they offer any other services (eg copy writing, taking phone calls) that may be useful to you.
In conclusion whether it is Twitter or Facebook you need to think about who you are promoting your product or services to and how you are doing it. While there may be people posting who say they can offer short-cuts it is better to develop your own long term strategy to develop your own social media "tribe" who will want to be a part of your team!