In the saiyan saga, it is CRUCIAL to get Ten and Kulilyn. They will be massively helpful not only against Nappa, being the two strongest if you level them up, other than Piccolo, but they make Namek much easier. In the Saiyan saga, level your party up until the fights stop. Ten should be around level 12 by the time you get to Nappa, with a bp around 1600. Kulilyn should be level 11 or 12, with a bp os 1300 or 1500, respectively. These two make surviving Nappa possible.