Making sure your espresso is great is hard work but I used to work at a coffee drive through. The general key is to not over steam the milk. There is some discussion on which way is best to add the espresso but there are a couple different ways. You can pour the milk in first then the espresso or you can pour them in at the same time. Never pour the espresso in first and then the milk. I don't know why but it sours it a bit and never tastes as fresh. Hope these tips help.
make sure you have good beans! a nicely roasted bean is very important. check around at some of your local coffee shops for some new espresso beans to try out, sometimes you'll find a gem!
I would say the tamping is the most important part, with the most variables that can effect your espresso. You must make sure the 'puck' of grounds is evenly distributed and packed.
REALLY keep in mind you want the whole puck to be as even as humanly possible because you want the water to move through the entire puck evenly. If the water finds a quick way through the grounds it will not brew right! And you will lose a lot of flavor/crema.
Gotta make sure the beans are ground just right, otherwise it won't brew correctly. Some grinders have an 'espresso' setting on them, some don't. If yours doesn't, take the grounds between your fingers.... they should be just just larger than a powder.... slightly granular. Mess around with the ground size, because it is very important to get it right if you want the right flavor!
Also, when you find the right size, try to keep it consistent every time. This will help you become more familiar with the machine and you will be able to adjust things here and there as needed.
I think a good espresso machine is extremely important here! Unfortunately, you will have to spend a lot of money to get one that delivers a good product consistently.... at least 500 dollars. But a good espresso machine will take a lot of guess work our of it and make your life quite a bit easier!
If you have a really high end machine you can teach a monkey to make espresso! Basically you just push a button and it does all the work for you. It will be better than an untrained barista, however probably not as good as a highly trained barista.
Making espresso is most certainly a delicate process.... one could almost call it an art form. While there are many many steps in the process that determine the quality of the end product, there are a couple of things I can point out to you right now that may help a bit.
Obviously, a nice roast is very important. A good french roast is my preference.
Make sure to heat up the machine properly first, otherwise it may not reach the temperatures needed for a proper brew.
It's also a good idea to heat up your cup first, so that you're not pouring your hot coffee into a cold cup. A lot of heat will be lost, and that a big part of the flavor. Luke warm coffee is sort of gross if you ask me.
The most important step of the process, though, is the tamping. If you own an espresso machine you probably own a tamper. It's very important to put the right amount of pressure on the grounds to ensure the perfect brew. You want to press firmly with the tamper... not so hard you hurt yourself, but enough to show the grounds who's boss. Also, I find it helps to do a little twist with the tamper at the end. This way, none of the grounds stick to it. If the grounds stick to it your nice, flat, freshly tampered grounds will have a little 'pot hole' in them here water can collect, which will cause imperfections in the brew.
Hope this helps a little bit. Every machine is different, so my best advice would be to practice a lot until you find the perfect method for you!