Do a large-ish partial water change first.
I would then get the water tested for everything before you buy fish. If ammonia/nitrites are at 0 (ask for a specific number not 'it's fine') and nitrates are reasonable (below 40), buy your first fish.
Monitor the levels daily for the next week, as mentioned. You will need to invest in a test kit - the liquid-based ones are best and a pH test is useful too.
If your tank is cycled, ammonia/nitrites should stay at 0 and nitrates should slowly increase. Whith one fish they shouldn't get too high so do a partial water change at the end of the week and you can then get your next fish. If, however, you find you get an ammonia or nitrite spike (it rises above 0), you will need to do lots of water changes every other day to keep it low and wait the 6 weeks or so ,I mentioned before, before getting any new fish.
You'll know your tank is cycled when ammonia/nitrites remain at 0. Water changes and plants should keep nitrates low. Once your tank is cycled, a nitrate test every week before a water change should be enough to show you whether you are keeping up with maintainance correctly (nitrates always under 40).
I would then get the water tested for everything before you buy fish. If ammonia/nitrites are at 0 (ask for a specific number not 'it's fine') and nitrates are reasonable (below 40), buy your first fish.
Monitor the levels daily for the next week, as mentioned. You will need to invest in a test kit - the liquid-based ones are best and a pH test is useful too.
If your tank is cycled, ammonia/nitrites should stay at 0 and nitrates should slowly increase. Whith one fish they shouldn't get too high so do a partial water change at the end of the week and you can then get your next fish. If, however, you find you get an ammonia or nitrite spike (it rises above 0), you will need to do lots of water changes every other day to keep it low and wait the 6 weeks or so ,I mentioned before, before getting any new fish.
You'll know your tank is cycled when ammonia/nitrites remain at 0. Water changes and plants should keep nitrates low. Once your tank is cycled, a nitrate test every week before a water change should be enough to show you whether you are keeping up with maintainance correctly (nitrates always under 40).