One of the most important concepts to understand in calisthenics is that of leverage.
Gradual systematic progressions are required to build to advanced skills such as the front lever, planche, or human flag. Start with a progression you can hold with good technique and advance by incrementally lengthening the lever arm. Practically, this involves starting with compact body positions such as the tuck and progressing to more extended positions such as the advanced tuck, straddle, single leg and straight body postures.
Here, the single leg front lever position is demonstrated.