I am definitely not an expert but all the below are the tips that I accumulate from all the days-long readings on CG and HB forum. Hope it helps and serves as a refresher if you've already known it. And I write this based on a HX machine like Oscar. But it applies to most machines anyway.
Some people like to leave the machine on for 24/7 so that it's ready all the time. But that will be more harmful to the machine in the long run. The seals will get really hot and shorten its life and the pressurestat will be cycled more often. So, I would recommend you to turn it on only if you need it. Let it heat up for 30min or more for good temperature stability.
Backflush is more to prevent the old coffee oil from contaminating your shots rather than to maintain the machine. But it's a good practice anyway. Backflush it with hot water at the end of everyday. Backflush with coffee detergent like Cafiza every 2 weeks to 1 month. I would recommend 1 month because too frequent detergent backflush would remove the oil out of seal and make it drier- shorter gasket life. Hot water is enough to get 99% oil out anyway. To backflush, just put a blind filter basket(without holes) and turn on the pump. After the pressure is built up(judged by quieter pump), then turn off the pump. Repeat this 2-3 times.
iii) Boiler flush
Boiler flushing is to get the water from the boiler with concentrated mineral to prevent scale build up. In HX machine, as you steam away, the steam evaporated as pure water- the mineral is left behind in the boiler. If we don't flush it out, the mineral will get more concentrated and it's prone to forming lime scale. I would recommend to do this every month, if you use fairly soft water and make maybe 3-4 cappuccino a day. To do this, just heat up the machine and turn off for 2 minutes. Then tilt the machine to the side of steamwand and open the valve. Water will come out from the boiler.Another way is to use the hot water tap if your machine have one, or the boiler drain.
iv) Use soft water
This depends on how hard is the water in your area. If it's hard, you need to soften it. Brita filter unfortunately doesn't work. It filters the water, but not soften it. If you don't have a water softener at home, I would recommend you using tap water+distilled water or tap water+ RO water. Mix them the in the ratio such that scale wouldn't form heavily and it's good enough for drinking. Using too soft water without mineral such as distilled water and RO water will make flatter tasting espresso. A mix of them would be the best. You can get the detail of your water hardness from your local bureau or something(google will help). My water hardness is 140-160ppm average so I mix with 1 tap water to 2 distilled water.
If you use soft water, then I wouldn't worry too much about descaling. Prevention is better than cure. Maybe descale in about 1 year if you use soft water, under home use(it's different for a commercial setting obviously). I highly recommend using soft water as prevention rather than to descale more frequently. Descaling involves more work and your precious time. But if you want to descale a HX, there's a very good post on home barista. http://www.home-barista.com/espresso-machines/simplified-hx-descale-t308...
Under whatever circumstances, don't run the pump continuously for too long. 1 minute is the limit if you want maximize the life of the pump. 30-40 seconds is the recommended from Ulka, but 1 minute is fine as mentioned by other experienced users on HB. Let it rest 1:30 minutes after 30-40 seconds. Avoid using hot water too because it can shorten the pump's life.
vii) Steam wand
Before steaming, make sure you bleed off the wet steam. After steaming, you MUST wipe it down and bleed the steam for 2 seconds to prevent any milk getting into the boiler, and to prevent dry milk from clogging steam tips. There is a one-way valve in the steam arm(for NS Oscar) so you don't have to worry too much about milk getting into boiler actually. But still, i would recommend making that into a habit. It applies to every espresso machine.
viii) Grouphead gasket
To prolong the life of the group gasket, don't leave the portafilter locked tightly in the grouphead after turning the machine off. You can either loosely engage it or just put it down all together. If the gasket feels hard when you lock in the portafilter, it's probably time to change it. This usually takes 1-2 years under light usage and provided you don't turn it on for 24/7.
It's a long list. But if you can follow all these, I assure your machine will stay happy for a really long time, like mine. =) If you truly care about the machine, all these will make sense and become natural to you.And not to mention your machine will reward you back by making great espresso. Haha!