I keep my ground coffee in the freezer, otherwise, once opened, I can taste it going stale within a week. However there is some dispute over whether this really helps.
Close the pack tightly, squeezing out air, and clip it shut with a bulldog clip or clothes peg to make it fairly airtight.
Unless you are a voracious coffee drinker, buy small packs that will get used up before they go stale. if you drink a lot of proper coffee, the caffeine might affect you and you might get the shakes, sleep and stomach problems, and a physical dependency that gives you a headache by morning when it has all gone. I used to and have cut down to a pint a week.
Beans stay fresher than ground, but the task of grinding them every day means most people end up not doing it.
Keep the coffee making equipment very clean. Unlike a teapot, stained old coffe pots impair the taste.
If you have not already got a cafetiere, you can use a teapot or jug. Stir several times then stand to let teh grounbds sink, and use a fine-mesh sieve/strainer.
Percolators and any other device that boil the coffee or keep it hot will spoil it.
I like Columbian blends, medium roast, not French or Italian which are dark roast and too bitter for me. "Which" tested ground coffee this month.
Asda Extra Special Fairtrade Colombian Roast and Ground Coffee (£2.78) and Taylors of Harrogate Guatemala Cloud Forests Ground Coffee (£3.59) tasted best
Rombouts was more expensive and not as good. Starbucks was very poor.