Blending teas isn't some sort of alchemy or anything. Blending is a nice name for mixing. Calling it blending might be good for marketing, but it's really quite simple.
It seems most tea people I know are fanatic about green and Oolong teas. They might drink black tea occasionally, but some have admitted to me in confidence that they really don't like black tea. I'm the opposite. I like green tea as well as black, but certainly not more.
I've mentioned this before, but this seems to be the obstacle to enjoying a good Assam for most people: the tannins. That musky, tart taste you get all the way down your throat when you drink it (but especially on the backside of your tongue) is what makes Assam unappetising for so many. But that's easy enough to deal with. You simply mix a tea with a high tannin content with one that is milder. Problem solved, yeah? Not quite.
Some others like (dare I say love) that tart slightly bitter taste. The objective for me when I blend these teas is to keep a bit of the bite but to temper it enough that a non-Assam drinker can enjoy it. That's where the milder Assams come in.
Before I get wrapped up in China blacks and Ceylons, I try to stay at least near the Assam family. Lately I've been using an Indonesian tea that is strong like an Assam but not malty. It blends beautifully to temper the natural qualities of a strong Assam.
When you're buying loose-leaf Assam, this is what you should look for. It's all about the colour of the tips of the leaves. Unlike many good Ceylons, which can be dark dark brown and have no other shades or colours, the Assams I like have light yellow or even red tips. I've had good ones that didn't-that were only deep dark brown. But that seems the exception rather than the rule.
Right now, I'm using Assam Khongea a lot to soften my stronger Assams. Hajua is good for this, too. Please, if you don't like malty, strong teas, don't spend too long here in this neighbourhood. Ceylons or Darjeelings are probably more your style.