Watching the Agung eruption unfold showed me firsthand some of the points of confusion when it comes to talking about volcanoes and eruptions. You can see the types of information and resources I gave during that time here. Below are resources that can help understand terminology and processes, and find authoritative sources of information. There are definitely more trustworthy websites than others and I provide them below. This is not a complete list and I will keep adding to it.
Communication is not my field of research (explosive volcanism is), this is purely based on my experience doing outreach on social media and working with media. If you have anything else that you would like to see added here, please let me know.
Firstly, what is a volcano? A volcano is an opening in the Earth where either solid, liquid, or gaseous materials come out of the Earth's surface (lava, ash, rocks, gas). More general information about volcanoes here.
For current Kilauea eruption information
Hawai'i County Civil defense updates
USGS Volcanoes Facebook page and Twitter account
USGS eruption updates
USGS fissure maps and multimedia updates
Volcanic history of Kilauea
Lava flow hazards and impacts
Kilauea volcanic smog (Vog) health hazards
Pacific Tsunami Warning Center
Public Map of fissures, road blocks, and subdivisions
Summary of the plumbing below Kilauea
Summary of the volcanic activity by USGS (4 May)
Big Island Video News is posting video from public meetings and official updates
Hawai'i Volcanoes National Park Service
Hawai'i SO2 forecast map
Volcano observatories around the world
It is important to report the information as it is given by the volcano observatory officials, or other authoritative sources. The term "imminent" should not be used unless the authorities explicitly state this term. Please also link to where people can find official updates for themselves. You can find the world's volcano observatories here:
World Organization of Volcano Observatories: Observatory Directory
Disaster agencies and other government organizations also communicate official information, such as BNPB in Indonesia, and many of these have Twitter and other social media accounts for rapidly disseminating information.
How are volcanoes monitored? Comprehensive monitoring provides timely warnings of volcano reawakening.
Where to find global volcano and eruption information
The first place I go to for information on a specific volcano and its eruptive history is the Smithsonian Global Volcano Program. You can use the search function to look up a volcano, and you can check here for the Smithsonian/USGS Weekly Volcanic Activity Reports.
For volcano terminology
USGS Volcano Hazards Program volcano terms glossary
GeoNet Volcano Glossary
Oregon State University Volcano Term Definitions
Information on volcano hazards and eruption processes
What are the different volcanic hazards? Learn more about what they are here.
Pyroclastic flows and lahars are two of the most dangerous and far-reaching hazards. There are videos on the hazards and impacts here, as well as volcanic gasses. These videos are presented in multiple languages.
Volcanoes do not produce smoke. The grey to white plumes we see are a mix of volcanic ash and gasses. You can find a wide range of volcanic ash information on what it is and how it affects different aspects of life from health to electronics here: Volcanic Ash Impacts & Mitigation.
Information on the health impacts and how to prepare for volcanic ash, including information pamphlets, can be found here: The International Volcanic Health Hazard Network. GNS Science also has a range of Ash Impact Posters for different sectors (e.g. water management, road management, airports, etc). GNS also has a Be Prepared: Volcanic Ash Fall page. VOG (volcanic smog) is a mix of aerosols and sulfur dioxide.
Ballistic projectiles, or volcanic rocks that are ejected out of a volcano, are a big hazard near volcanic vents. More information on distributions, impacts, hazards, risk, and methods of communicating and managing the risk can be found here: The Communication and Risk Management of Volcanic Ballistic Hazards.
There is a lot of uncertainty involved with volcano forecasting. The magmatic/volcanic system is constantly changing and volcanologists use the monitoring tools, local knowledge of a specific volcano, and cumulative global volcanology scientific understanding to give forecasts of activity. You can read more about that here: 'VHP uses monitoring data and volcanic history to forecast eruptions'.
A great case study that demonstrates how much volcanic activity can fluctuate leading to an eruption (or no eruption) can be seen in this NOVA video of the 1991 Pinatubo eruption:
"Approximately 800 million people live within 100 km of active volcanoes worldwide". Here is a Global Volcanic Hazards and Risk report that discusses the hazards and risks posed to populations by volcanoes with case studies.
Yet is important to understand how volcanoes can physically harm people, and at what distances from volcanoes. You can get information on that here: Volcanic fatalities database: analysis of volcanic threat with distance and victim classification.
The Volcanic Ash Advisory Centers (VAAC) give information on volcanic ash plumes for the aviation industry and is a good place for latest reports.
Additional volcanology projects that have resources and information:
DEVORA: Determining Volcanic Risk in Auckland
STREVA: Strengthening Resilience in Volcanic Areas
Yellowstone Volcano Observatory Blog Posts and Frequently Asked Questions.