NASB: "Let us hold fast the confession of our hope without wavering, for He who promised is faithful; and let us consider how to stimulate one another to love and good deeds, not forsaking our own assembling together, as is the habit of some, but encouraging one another; and all the more as you see the day drawing near."
The Messege: "Let's keep a firm grip on the promises that keep us going. He always keeps his word. Let's see how inventive we can be in encouraging love and helping out, not avoiding worshiping together as some do but spurring each other on, especially as we see the big Day approaching."
So first off, people say that you have to meet (assemble) together; and when they say that, they always have in mind what a meeting is, whether it entails a certain kind of building, or someone gives a speech while you sit in uncomfortable chairs looking at the back of someone's head, OR they mean you must pray or study the Bible or sing songs togther in order for it to be a real church meeting.
What the passage does say is that you should not give up on meeting altogether, period. That's what forsake means. Don't avoid worshiping together, the passage says. The passage says that we need to gather to encourage one another and stimulate each other towards good deeds. These are the only descriptions here of what an assembly is like or is.
The context of the book of Hebrews is Christians under persecution. These people needed to get togther and encourage each other. The author is saying,
"hang on to the Lord and His word and your hope in Him, He is faithful. Think of ways that you can bless each other in word and deed. Don't isolate like some silly folks do, but take risks and reach out and open up to others. We need each other."