There is no right or wrong way to do this.
Say it three times, with feeling.
This is important stuff, as what will happen over the course of your journey will be a process of discovering your way. You will grow in intuition, knowledge and skill; you may get stressed, you will have joy. Accidents will happen with messy outcomes, wondeful outcomes, and sometimes both at once. There is no right or wrong way to do this.
So here's a condensation of some hive-mind wisdom to help you get started out. I've made it a 'how-to' for ease of writing only. You must decide (see the Disclaimer again if you need to) what is right for you.
BEFORE YOU START
You must consider your approach to the relevant medical providers. Except in some sensitive inpatient situations you do not need to ask permission to feed yourself, your child or your loved one as you best see fit. Carefully explained and well handled, you will likely (but possibly won't) find support and help at hand from the dietitians, doctors and other providers around you. Like most humans, most of them actually care, and just want to know that you really are trying to do your best here. Remember they deal with all sorts of odd people, so their suspicion is understandable. If you are relying on them for medical help, it makes perfect sense that they know what your nutrition and feeding plans are, just as they need to know what medications are being used. This is very important, OK?
1) You will need a blender.
See the Blenders and Blending page for this.
2) Decide how you're going to begin the transition.
There are lots of necessarily individual factors to consider here. Firstly:
2.1) What is the status quo?
Are you going from oral eating to tube feeding? Formula to BD? Breast milk (BM) to BD? What do you know about food intolerances? What don't you know about food intolerances? What are the 'medical' parameters you are working with? Sounds obvious, but important nonetheless.
2.2) Make an initial plan.
Let's say you're starting an infant, transitioning from BM. You'd probably do what you'd do for an oral eating child, and start with just the one ingredient at a time to 'screen' for food intolerances. So plan to do a simple vegetable or fruit feed in between BM feeds maybe. Or blend with a little expressed BM. On the other hand, you might know what food allergies and intolerances exist (or existed prior) with a formula-fed scenario, so you could plan a balanced meal blend to replace a formula feed, looking over time to replace some, many, or all formula feeds.
NOTE: some people have used formula as a base for blends, especially in transition. it has worked OK for some. From what I understand, it more often than not is problematic - it may not blend well for some reason, and you do not get to see/feel the differences in not having formula in the body, so it's counterproductive in that way.
2.2.2) Cold turkey.
Takes some courage, for sure, but then there are those who have come to BD like refugees, needing to escape a bad situation with formula intolerances, weight problems, and all manner of hard stuff to deal with. Some of them just jumped in and have done super. Others one day actually read the back of the can and said "no more". It's your call, and there have been as many great experiences as 'interesting' ones. Remember, very few decisions in life have permanent consequences anyway.
3) To count, or not to count?
Decide on the calorie and nutrient calculation question.
If you're going to be providing a meal plan to a dietitian or doctor, or want to be sure you're making good, complete, balanced blends, then you're going to want to do some calculating. There are eleventyhundred sites out there on the interwebs that can help, and these will over time be posted on the Links page (send me your favourites and I'll pop them up there!). It's easier than you might fear.
3.2) Not counting.
If for example you're still going to be using formula for feeds as well as BD, then counting is not as necessary. I don't count, but I did in the past, just to make sure. Most oral eaters don't count calories, and many people just simply blend what an ordinary mouth-eater would eat. No problem. A lot of this stuff depends on the questions above and medical parameters involved.
4) What to blend?
The world's your oyster. Although if you're blending oysters I'd shuck them first. To start out, there are three basic ways to go:
4.1) A regular meal.
Appropriate for some, you simply take what the tube-fed person would eat if they ate, and blend it.
4.2) A simple or singular blend.
If you're doing an elimination diet for intolerances then you'll be starting out simple, or if a delicate digestive system is involved you might want to do a bland blend like banana, rice, and applesauce. See below also.
4.3) A Recipe.
I'm not posting up recipes right now, but I will be doing so as blog posts. They will be labelled and searchable. There will be many LINKS. Groups like the Blenderized Diet Group have amazing archives of recipes and books like Marsha Dunn Klein's Homemade Blenderized Diet Handbook (which I've not read) apparently are well worth it too. Or just make up your own.
5) Make your first blend. Exciting!
Um, yes. See the Blenders and Blending page for more blender-wrangling tips.
Most people make smaller blends at first, progressing up to bigger ones as confidence grows. Think of it as food, yes? This means freezing if it's going to be around more than a day or so, and refrigerating otherwise. Everyone has their own favourite methods of storage (I use 450 ml squeezy bottles mainly) and you'll find one that suits your needs. One that sounds brilliant but that I have yet to try is using freezer bags (i know, why didn't I think of that??) because you can squeeze the air out, they sit flat so don't take up much space in the freezer, and the larger surface area makes defrosting faster. Whatever you do, just make sure you observe proper hygiene rules.