Most wire distribution services charge by blocks of 375 or 400 words. That includes title, a brief summary, body of the release and contact information. If the release is more than the word limit, you will be charged extra per 100 words. Images, video, documents or podcasts are also charged extra. But many online PR distribution sites do not have the typical 400 words limit. Image and document attachment is also commonly provided with the basic service.
Before turning loose your press release, decide where you will make the most impact. Wire distribution services classify a press release into:

1) National Release: Targets all national media outlets for a particular industry like Automotive. Consumer, Sports, Technology or Travel.

2) Regional Release: The four main regions are Northeast (includes New York and New Jersey). Southeast (includes Florida and Virginia). Midwest (includes Illinois and Ohio) and West/Southwest (includes California and Texas).

3) State and Local Release: New York State and New York Metro can be two different options. In general, New York-related distribution is expensive, because of the high number of media outlets in the region.

4) International Release: Again, there are man classifications and sub-classifications of an international release based on countries and/or continents.
Apart from the above categories, some wire services also target Hispanic, African-American and North American Chinese media outlets.

Keep in mind that you should draft and submit your press release two days in advance, because most wire services will call for a verbal confirmation before distributing.

With online services you can specify 5-10 industries to target. By default, the region is set to global but if your release applies to a specific city or region, you need to choose the appropriate setting. Any journalists or bloggers who have subscribed to releases for that region will then receive your release.

Now that you have decided what type of distribution service you will use and where you will target your audience, its time for the most important part - creating an effective, compelling press releases.