Stamina and technique. Dalasan mo yung pagbabike para lumakas resistensya mo, and to build those muscles. Set a goal kung ilang km/s week and kung anong time. Try going for longer distances/shorter times.
Find your comfortable cadence, tapos make sure yung gear ratio mo matches your preferred cadence pag paahon.
Make sure relaxed yung upper body mo, kasi kapag tense yon, mapapagod ka kaagad. One way to know na relaxed yung upper body mo kapag umaahon ka is kung kaya mong umahon gamit isang kamay lansalam