Press conferences are usually hosted by organizations or celebrities to announce something that was not known before. Something new. Something that just came up. Something they would like you to write about. Sometimes with just the intention of making some noise and garnering some attention, and sometimes to really get feedback on what they are doing and what people think or feel about it.
If you are a well connected writer, you will probably get the invitation to the press conference directly from the organization or the agency handling the events and public relations for said party. It is typically in the form of an email stating the date, time and venue for the presscon, the speaker/s and who they are - designation, organization, cause, accomplishments, etc. and the topic to be covered at the event. Most times this will have some background on what is being addressed, especially if it is a current issue or a new product, or new features to a product, or a reaction to an incident. Other times though, they try to leave in some suspense and excitement in not telling you exactly what it is about.
Either ways, do some research on the organizations and speakers so you know why you are headed there. If you are really close to the folks that invited you, it wouldn't harm to ask them for a titbit on what this is about. And do confirm if you are attending, yes please do! This will help the organizers tremendously when they have to consider the logistics of the presscon- parking, seating arrangements, food and drink, handouts, giveaways, promotionals, etc.
When you head for the press conference, make it a point to say hello and thank your contact who invited you to the event. Surely they thought you a valuable resource to invite you instead of just mailing you some information after. Look around at the venue and try to get a spot as close as you comfortably can to the speaker so you can focus on what you are there for and you can hear them loud and clear to get pointers for your article. Take notes while they speak and graciously accept any informational fliers or press kits given to you. They usually contain the information you need when you later remember you forgot to note down some details!
If you have questions, just ask, but only if you are aware of the topic at hand. If this is not your subject area of expertise, then better to hold on till you can get back to your work desk, do some more research and then reach out to the agency with your questions as a follow through to your visit. They will usually be very happy to get your answers to you. If you have questions that have not been asked at the presscon by other attendees, then that might make for a good question or two to ask directly to the speaker/s. This way, you will have exclusive sound bytes for your media outlet. Ask your contact to connect you with the speaker/s immediately at the venue itself, or ask if they can be reached later with some questions you had specifically for your publication. Again, most often than not, they will gladly oblige. I am yet to come across somebody that organized a press conference and then refused to answer additional questions!
Most presscons will include some food and drink, maybe some passed bites and beverages. Help yourself to some but don't eat for the rest of the week at this one event! Presscons usually also involve some small promotional gifts for attendees. Usually this is very subtly included in the press kits, but sometimes these are bigger giveaways and have to be presented individually...use your best judgement on whether you want to walk out with that or not. I have had events where these promotionals had nothing to do with the speaker or organization, but were just a way to say thank you in advance if you chose to write about the presscon. I would typically graciously say thanks and leave, but on the other hand, sometimes, those giveaways have to do with the company or product directly, and I would go ahead and take/ask for one just in case it helps add more information to my written piece.
Always arrive with plenty of time to spare before and after the presscon, unless, of course, the news is just so earth-shatteringly urgent, that you simply have to rush out and get it up on your blog or site asap. Keep time to exchange pleasantries with industry colleagues you happen to run into. Certainly try to get a few minutes at the end with your contact who invited you to the presscon. Sometimes, letting them know which outlets you will cover the event for, especially if you are a freelancer, helps them know you did not just come on over for a fun evening! Be professional about it and you will find yourself invited to more such official occasions to write about.
If and when any publications you write for do feature this announcement, be sure to send a link or a pdf image of your article to the agency, individual, organization, or speaker - whoever your contact is, so the exercise comes full circle. They know to trust you now as someone that will try to get them exposure to the audiences they are targeting. And you can rest assured they will keep you top of mind for other stories that can get you a byline in your desired media outlets.