hmmmm, to "taste like beef," ....
If you're cooking it from scratch, you can infuse the seasonings you want into the mix when you form the "dough." This is where the experts can really get it to taste, look and feel exactly like the meat produc they ar emimicking. I'm not that good at it yet, but it is still very yummy.
After it's initally cooked, or if you buy it already prepared, then you could try braising it in liquid smoke or any barbecue sauce that you like. Maybe even some shoyu (soy sauce), or again try the tamari sauce. Or heck, put some A1 sauce on it!
You could also add any dry spice rub. Unless I make my own spice mix, some of the Mrs. dash salt-free varieties like the carribean, extra spicy or lime are good. They make an orange one that could taste good by adding the citrus. If you cube it and sir fry it, you could make it taste like Chinese orange beef, especially if you add brocoli.
The thing I like about seitan is that, although it has its own distinct flavor, it is like tofu, in that it takes on the flavor of what you make it with, ie sauce, etc.
One caution is that if you make it from scratch, you don't want to over work it or over cook it, because it can become tough. Similarly, once you have initially cooked it and you're ready to use it in another preparation, you also need to be careful about overdoing it by having it on the heat too long as it will get tough as well.
Hope this helps, have fun!