Start with good ingredients. Use fresh or frozen produce and quality powders and oils. I'll be honest, it takes a lot of work to mask the taste of a nasty protein powder and you can never really hide the grit. I usually use an unflavoured or vanilla whey powder, as I find they give me the most versatility.
I find it best to freeze some ingredients first, usually I choose the fruit. If you want, you can use ice cubes to make it cold, but remember that they add to the overall volume of the drink, so adjust yourself accordingly.
If you want your drink to be smooth and creamy, make sure you're using some soluble fibre. The banana is the gold standard here and is also popular for its sweetness, but you can choose berries, passion fruit, and oranges to help improve texture. Another option is to use about one tablespoon of ground chia seeds per serving. You want to make sure they're ground first, so they don't just stick to the sides of the blender and your glass. They also pack in a ton of nutrition and healthy oils, so why not.
If you're looking for a silky texture, you may want to add in some healthy fat. Here, half an avocado works wonders, and it's also a source of soluble fibre, so it does double duty. You can also use a bit of your favorite nut butter or some coconut oil. Also, consider your main liquid. I generally use water, but if you prefer, you can try almond milk or coconut milk for an even smoother experience.
So, what about sweetness? A lot of recipes call for a bit of honey or stevia and that works, but I prefer to get my sweetness from the fruit I use. In the off chance I'm not using fruit , making a chocolate shake, for example, I'd probably choose a banana or a few dates to sweeten the drink naturally. If you're looking to mask a taste you really don't enjoy, pineapple is your new best friend. It carries a lot of sweetness and helps to cover up the ick quite well.
Now, the process. I like to start with my liquid and then add my frozen fruit, so it has a chance to thaw and cool the liquid as I add everything else. However, if I'm using a lot of greens or other vegetables, I'll use the blender to chop those up first, using just enough liquid to get the job done. Then I'll add in the fruit, seeds, oils and so on. I generally chop again, then switch to a blend or puree setting, after everything starts to look pretty uniform. If you find you have too much liquid in the end, again, the fibre can help to absorb this, so toss in a few more berries, or seeds and blend some more. If your drink is too thick, that's an easy fix, just add a bit more milk or water and blend again. Only use a small amount and keep blending to check for consistency, it's very easy to over do it.
And that's about it. If you're lucky, you'll come up with something that's both nutritious and delicious maybe resembling the drink below. Can you think of anything I missed? Feel free to tell me your smoothie best practices in the comments below.