Research the area to see if the things you want (supermarkets, bars, idk) are nearby, as well as the prices of apartments nearby so you'll know the price is reasonable.

Ask about maintenance charges and whether it's included in the price or not.

Don't appear too enthusiastic even if you love it so you can drive a hard bargain later. You could say things like "Oh I like it but I don't like the color/I'll have to fix this and that" or something.