Well...first come up with a sort of homemade Rotel - using some crushed tomatoes (if you like that in your queso), and maybe sauté some onions & chillies in just a wee bit of oil - not much because you want something not too greasy. Then I'd make the cheese sauce and add the tomatoes/onions/chillies in.
Or if you didn't fancy doing the above, you could just experiment with adding spices like chilli powder.
This is my cheese sauce, which is the same sauce I use for Mac & Cheese (I would have used Velveeta for both mac & cheese and also for queso in the US) - only for queso, make sure it's on the thicker side (less milk, if it gets too thick, you can always dribble in more milk):
Grate block of Red Leicester or Double Gloucester cheese (about 250-300 g size).
Melt 3 Tablespoons butter in a saucepan & add 3 Tablespoons flour to make a roux. Cook it, stirring constantly, until it browns just a bit. Add about 1 1/2 cups milk - slowly, a bit of milk at a time, stirring constantly to dissolve the roux bits & not be lumpy. Season with salt & pepper to taste. When that's all smooth, and the milk gets steamy, start dumping in the grated cheese & stirring it gradually in until all melted. Add a bit more milk if you think it's too thick.
Most of the Tex-Mex food I cook tends to be an experiment, in terms of using the ingredients available here to replicate something I would have made in the US - fortunately, it usually turns out fine! Like I made green chile gravy yesterday for the green chile & sour cream chicken enchiladas & I was worried it was going to be bad, but once it was all together with the enchiladas - it was fab!
