There are different ways to structure a dream sequence. The most common is to create a "frame" around it at the beginning and end of the scene, for example showing the character in bed, then the dream, then waking up. However, sometimes the top of the frame would be a spoiler, so you need to consider other options.
If you're in the middle of a longer work, and readers already know that certain things have happened, suddenly switching those details can clue that this is a dream or flashback scene. This works fine for a few paragraphs, but if it runs longer, readers may start doubting their belief that this is a dream sequence, which can get distracting.
So another way to confirm the framework would be to use the word "dream" after a few paragraphs: "In the way of dreams, she was suddenly outdoors ..." That would let you support the scene without adding a lot of length or being obtrusive about it.
As an alternative to putting the frame at both top and bottom, you could also remove it entirely and just say in the header, "This is a dream sequence." Online, you could write flashback scenes that happened earlier, as separate installments, marked as such. The format of a longer story told in multiple posts gives you a lot of flexibility. You have to account for it, though -- reading the same scene in a whole novel, it might work because the size of the dream scene would be much smaller than the rest of the book. But in a short post, the dream scene may be longer than the waking part, and thus feels top-heavy.
A good way to practice dream scenes is simply to write a bunch of them. Try on different lengths, types of framing, and other techniques. Make a bingo card if you need inspiration. Some references:
This article goes into detail about how to make dreams plausible:
Here you get lots of information about how sleep and dreams work, as applied to fiction:
This is a general discussion of dream scenes and how they work (or don't):
Try three ways of aggravating your character with dreams:
Here is an analysis of a famous dream scene and an exercise to write your own:
This one gives you step-by-step instructions with space to write:
Finally, take a look at the creation of cinematic dream scenes:
That should give you some very different ideas of why and how to present a dream sequence. Experiment. Try them on. See which ones fit yourself as a writer and your characters.
This got me thinking I should mention dreams in the Iron Horses series. I've been at that one a while and I don't think it's come up yet, which is ... oops, pretty unrealistic in a culture where people routinely talk about dreams over the breakfast table. Not to mention anyone thrown out of a truck into a barbed wire fence will start having nightmares after recovering enough energy to process the trauma.
So that raises the issue of how different dreams can be. Most Native American tribes place great importance on dreams, and will classify them in different ways -- everyday dreams that replay recent memories, hint dreams where something happens that gives them an idea, vision dreams they can make sense of themselves, and bizarre dreams that make so little sense that a shaman's help is required for interpretation. For instance, a tribal dreamer is likely to pay close attention to plants and animals in a dream, whereas most Americans would notice cars and buildings. Even if they both saw a dandelion growing through a cracked sidewalk, the Indian would talk about dandelion medicine and the white person would talk about urban decay. Talking animals are quite routine in native dreams, and not considered weird; if a bird tells you to go wash your car, then after you wake up, you'll probably just do that and not think anything of it. But to a white person that would sound weird -- even if the same person is prone to surrealist dreams of dancing lampshades and thinks they're funny.
For comparison, here is a standard dream dictionary and a sample of Native American symbolism regarding animals. Of course, the same animal can be a positive figure in one tribe but negative in another, the same way that Christian may think of black cats as unlucky but Pagans consider them lucky. In this regard, both the content of a dream and the character's response to it can show a lot about their personality and background.
Do you enjoy reading/writing dream scenes, or find them a distraction?