1. Get a pair of digital scales (learn to use the tare button) and spend half an hour making coffee of different strengths. Decide which you prefer and then always use that coffee to water ratio when you make it.
2. Get some decent coffee. You can get a grinder if you want, but it won't make as much of a difference as just getting it from a good source. It can be freshly roasted, freshly ground, whatever - just get it from a good place, not from a supermarket. Personally, I buy a kilogram of coffee beans from http://liminicoffee.co.uk/ once a month. I used to buy it weekly from http://pactcoffee.com/ but I found it's more convenient and just as tasty to get it delivered monthly.
Optional third improvement:
3. Get an Aeropress or a Chemex (my preference is a Chemex - even easier to clean up than an Aeropress, can make multiple cups and can be kept warm if you have a hotplate, although I wouldn't recommend that). This is a good step but won't make as much of a difference as picking good coffee and measuring the amounts you're using.
There are so many optimisations you can do. Most of them won't have too much of an effect. I do them anyway - I have all of the equipment, have a fairly expensive grinder, spend time letting the coffee bloom (I swear that's rubbish) and am planning to roast my own beans soon - but they're by no means necessary. Do those two things first and then stop to see if you're satisfied.