For me, best practice is to just have cells on your sheet that calculate the first and last row (different ways you can do that), then give those cells a range name such as FirstRow and LastRow. In your vba then you refer to these cells to make your code dynamic.
e.g:
firstRow = Range("FirstRow)
lastRow = Range("lastRow")
test = range(cells(firstRow,lastRow))
-- Note I have not written VBA in many many years so am writing the above from memory so it may be not be exact.
Of course you can do it all entirely in VBA using the xlDown method mentioned previously but I prefer the transparency of it being on the main page so that easily spot if something breaks.