One of the most important rules in helping neighbours is simple: Offer specifically, respect the answer, and don't take on more than is safe for you.
Knocking And Checking In
Identify yourself clearly and explain why you're checking in ("Hi, I'm from down the street, just making sure everyone's okay")
Keep it brief and low-pressure
Ask an open question rather than assuming what they need
Offering Help
Be specific rather than vague ("Can I bring you some water?" rather than "Let me know if you need anything")
Respect a "no thank you" without pushing further
Only take on what you can reasonably and safely provide
Connecting Them To More Help
Share information about warming/cooling centres, shelters, or community resources if relevant
Help them contact family, a neighbour, or a support line if they'd like that
If the situation is beyond what a neighbour can help with, encourage them to call 911 or have you call on their behalf
Looking After Yourself Too
Helping a neighbour shouldn't come at the cost of your own safety. If a situation feels like more than you can safely handle alone, that's exactly when to call for backup - family, other neighbours, or emergency services.
Insight
A brief, respectful check-in is often all it takes. You don't need to solve someone's whole situation - you just need to make sure they're not facing it alone.