The only caveat: be patient. Give yourself time to experiment, knowing that some factors are tough to control at the micro level, like lot-to-lot variations—no two harvests are ever the same—and roasting and freshness dynamics. Consistency is going to be your biggest challenge: something that larger-scale blend makers work endlessly to perfect.
Let's start by looking at single-origin dynamics, where wine offers so many rich and relevant analogs. Grapes like Merlot and Cabernet Sauvignon mature into beautiful wines all their own, while melding with other grapes to weave rich tapestries like Bordeaux. My homeland's Sangiovese and Canaiolo grapes are wonderful as their own wines, and lend distinct characteristics along with other vine-ripened cousins to Chianti. The list goes on. Each grape has signature characteristics born of genotype and growing environment. That's why a top Pinot Noir from Oregon offers a decidedly different tasting experience from one produced in France. Oregon's volcanic soil imbues Pinot Noir grapes with more sweetness and fruity notes than their Burgundy-grown cousins.
So it is with Arabica coffee. A Bourbon bean, for example, grown in Brazil yields aromatic and flavor characteristics different from of its cousins grown in East Africa, El Salvadora, or Guatemala. Key environmental factors contributing to regional variations include soil type (pH and mineral content); climate (temperature, humidity, and rainfall); altitude; and latitude. Root depth, water depth, drainage, and other crop types planted nearby are just a few of the other variables.
All that said, there's nothing like poor processing to undo most or all the great effects of good breeding and favorable growing conditions on coffee. (More about this below.)
Okay, science and geography lessons over! Let's develop a basic blend well suited to espresso preparation. We'll need to ensure three key characteristics: good body; the right balance of bitter, acid (not the sourness of an unripe fruit but the pleasant sourness of, for example, a perfectly ripe orange), and sweet; and not least, lots of aromas.
An excellent Brazilian natural Santos (two terrific producers: Sul de Minas and Cerrado) makes a great base for a blend, producing good body thanks to high presence of soluble solids, along with a little sweetness and perfect bitterness—if the roast isn't too dark (beware!). Chocolate and caramel are most prevalent among aromas. You can also use a good Indian natural bean, as your base, similar to the Brazilian Santos, with a light spicy note, but less sweetness. Try Indian Natural Cherry.
For the right amount of sweetness, I like washed Costa Rican Tarrazu and West Valley, and beans from other high-quality Central America coffee-growing areas in Guatemala, El Salvador, Panama, and beyond. Many high-quality coffees from these regions will provide proper sweetness, with a pleasant, wine-like acidity and wonderful fruit and toasted bread notes.