The most important thing is, be flexible and try to be patient. Disasters are, in all senses of the word, chaotic. In disaster relief circles, the first wave of volunteers is sometimes called “the disaster after the disaster” because before they even know where to put all the survivors, before they even have a plan to coordinate all the volunteers, there's thousands of volunteers ready to be put to work. Also, remember the recovery after a disaster can take years and sometimes when the community needs you most is actually a few months or even a year after a disaster, because most other potential volunteers are no longer interested.
Sometimes the best thing to do directly after a disaster is to make contact with an organization already there and figure out their biggest needs (generators, ice, basic first-aid supplies, or sometimes the biggest need is just money). I know it may seem boring or unfulfilling to just raise money, but keep in mind that the church or mosque or whatever probably didn't factor sheltering dozens of survivors or feeding volunteers into their budgets, so money may be the thing they need most. Also, by giving them money, they can then spend it in the local economy, an economy which was very disrupted and lost a lot of money because of the disaster.
Contact and coordinate your efforts with people/organizations already at the scene. It may be that most areas are still locked-down and no one is allowed in, so there's not much volunteers can do. Also, try and figure out if there are age restrictions, if minors need a guardian present or a written consent form from a guardian. Someone who is actually there can also give you the areas where volunteers are needed (doing actual clean-up, donations sorting, data entry, etc) and tell you what type of clothing to wear. Some volunteers who wanted to do clean-up in Joplin came without close-toed shoes and it was too much of a hazard to have them in the field, so they had to volunteer in areas that they didn't really want to. Also in Joplin, we had EMTs, Firefighters, etc. coming to our volunteer center and demanding to be a part of the search and rescue. They are pretty careful who they allow on those teams, so this is something you should try and work out beforehand (for instance, if you're a firefighter, then try to call the local fire department in that area). It is also important to bring your id, certification, license, etc. if you are wanting to volunteer is a specialized capacity.
Make sure to work out beforehand all of your logistics (place to stay, food/water, bedding). As a volunteer you have to keep in mind that, because there was a disaster, most of the local resources are rapidly being exhausted and if you come unprepared and ill-equipped you can actually be more of a burden than a help. I remember a few times when food was supposed to be provided in disaster areas, but tornadoes have a way of making street signs disappear and cause landmarks to not be in their proper place, so meeting points are missed or misunderstood. You will have a better experience as a volunteer if you are thoroughly prepared.
While on the subject of food, if you have a food truck, a huge grill, or another thing of that nature and want to help provide food for volunteers, keep in mind that you will probably have to work things out with the health department. We had many well-meaning individuals who came a long way to Joplin who wished to set up and provide food for survivors and volunteers, only to be shut down by the health department because they weren't where they were supposed to be, didn't ask for permission, etc.
When trying to figure out needs, whether for volunteers or donations, don't solely depend on the media for information, because they often get misinformation (sometimes from well-meaning individuals) and/or do not share the whole story. Or the media makes an announcement for a need and doesn't realize that some company was generous enough to fulfill the whole need, so then there is an excess of that one item. Sometimes the media isn't allowed access to areas where heavily involved individuals are (people who actually know what's going on), so they ask whoever they can talk to, which is sometimes a volunteer who has only been there an hour or survivor who hasn't left the area of the emergency shelter since they got there.
Lastly, and very importantly, try and figure out if the community is keeping track of volunteer hours and equipment used in volunteer efforts. You can normally find this out by contacting someone in city hall, possibly looking on the community's website, or sometimes the media will announce it. If FEMA declares a disaster then the federal government does a cost share (the local government pays a percentage and the federal government pays a percentage) for the disaster recovery. Volunteer hours and equipment used can be given a dollar amount and be counted towards the percentage the local government has to pay. In other words, as well as your volunteering physically helping recover the disaster area, it can help it financially recover as well.
Thank you for your willingness to volunteer and I hope you have a wonderful volunteer experience. Be safe, work hard, maybe have some fun, and create some fulfilling memories. God bless, may he give your hands strength and may he comfort the survivors.