I have just moved into a new apartment on the fifth floor of a building and the water pressure is dismal. The sinks I can deal with, but not the shower... are there any hacks you can perform on the shower head itself?
If you get a narrower head, the water will come out faster, so it will feel like there is higher pressure, even though the water is low in volume. You can even get a head that puts the water out in one narrow stream, which can be quite sharp.
There's nothing you can do to improve the pressure in an apartment complex, other than trying to get your shower at a time when everyone else is not likely to be running water. Showers, dishwashers, and washing machines (not everyone has these last 2) use a lot of water, so 2 running at once will not improve your experience.
Remove flow-rate restrictors in the shower head
You can make sure that there are no water flow rate restrictors inside the shower head. These can usually be pried out (I've done this on hand-held shower heads, too; see also this video):
Or you might need to drill a bigger hole in the water inlet of the shower head (which I've done on larger shower heads).
Remove restrictors in the shower valve / install bigger plumbing
Even if you hack the shower head itself, your flow rate might be limited by the piping / valve of the shower itself (cf. this video).
Also, in the U.S., it's federal law that shower heads must be rated < 2½ gallons per minute! See Jeff Tucker's Hack Your Showerhead: Or How to Get the Government Out of Your Home and article.
Some shower heads have screen strainers in them, to prevent grit in the pipes from clogging the spray nozzles. unscrew the shower head from the pipe and check for the presence of a clogged screen. it can be unclogged by pushing the grit out of the pores using a needle.
Use a water heater which has a storage tank that is big enough for your shower needs.
Those storage tanks used to be the rules in the past, so you should be able to find them in many countries.
The life hack solution might be to install a tank or even a tub high enough inside your bathroom that you can run a shower from it, fill it with water to your chosen temperature and run a shower from it.
If just gravity is not enough to get your the required pressure you can think about installing a pump and/or a container under pressure.
Of course, these are solutions for when a change to your shower head does not give the required results.