1. Unless you live in an area where limescale isn't an issue, use a bottled water with the lowest 'dry residue' value that you can find. I use the 'SPA' brand as it has a 'dry residue' value of 33mg/L and is available in 3L bottles at my local supermarket. It is important that you check this figure carefully as many bottled waters will have very high dry residue value (for example 150mg/L or more), which will quickly degrade the performance of your machine in the same way that tap water with a high limescale content will.
2. This point is absolutely fundamental: GROUND COFFEE IS A WASTE OF MONEY. Ground coffee becomes stale after about 30 minutes of being ground. Freshly roasted coffee beans give off gas for up to 48 hours after roasting. For this reason a vaccum packed brick of ground coffee will never be fresh, because if it had been bagged when fresh it would re-inflate the vaccum packed brick. Ground coffee is sold because it is a convenience product (the root of all evil, but more on the virtues of slow food in another post when time permits).
3. You will never make a decent espresso with pre-ground coffee. Conclusion: you must buy a burr grinder. I would even go further and say that if you want to make great coffee and cannot afford an espresso machine and a grinder, buy a grinder first then add the espresso machine when you can afford it. Strange but true ~ you can make superb coffee with a £5 filter cup & disposable paper filters. Sure, it won't be espresso, but a superb cup of filter coffee can still be a delight to the senses.
4. Now that you have a burr grinder you need to get the grind size just right. It is important to state from the outset that grind size and tamp pressure ( how hard you compact the grinds into the portafilter) go hand in hand. By that I mean that if your grinds are towards the large end of the scale for espresso production you will need to exert more pressure with the tamp. Conversely, a fine grind means less pressure on the tamp. It is personal preference only, but I grind fine and apply only very light pressure to the tamp. With Londinium espresso beans you will also need less pressure than most