When laning with Trundle, you always want to take advantage of his passive(King's Tribute) meaning try to stay close to as many dying enemy minions as possible in order to restore your health. Don't be to aggresive because you are very squishy until you get Phage.
Focus on farming and poke your opponents with your Q when that's possible. Always be carefull not to get damage back.

Same as above. Take advantage of your passive so you can limit your trips back to base for health and rush yourself to an early vampiric scepter for early independensy.

Every game I played with trundle I can never finish my build cause I always rule without the last 2 items (Infinity and Sunfire)

I thought of adding the Infinity Edge to increase my AD and Sunfire for the Life Boost and cause it turns you into a Super Saiyan. meaning you are more resistant to damage.