Keep in mind that you will want to use your primary school's attack most of the time. The reason for that is because your power pips only count as 2 pips when using cards from your primary school. Your blades and traps are usually for your primary school. Your equipment usually boost damage only to your primary school.
What you want to do is choose your secondary school for items that they have that either enhance your primary, or to fill in what your primary school is lacking.
Since Life is of the Spirit schools (Life, Death, Myth), you have no defenses from the Elemental schools (Ice, Fire, Storm). I would suggest learning Ice up to Tower Shield. This will also give your their Fire/Storm shield (the 2 strongest of the Elemental schools).
Let's face it, Life attack spells aren't that strong. There is a 2-part solution to enhancing the damage that Life dishes out. The first is to learn the Spirit Blades and Spirit Traps from Niles the Balance tree in Krokotopia. The second, which takes longer, is to learn Death up to Feint. Feint's +70 trap is a real damage booster. These additional blades and traps can be used with Life's regular blade and traps for awesome boosts in damage.