Sometimes there's more than one way to skin a cat. To make a result more powerful might not always mean increasing a skill degree. Skill degrees can get pretty pricey at high degrees, so often it might be better to choose and advance a different skill that also gets the job done. For example, a fighter might choose to increase his brute strength rather than increase his swordfighting skill because both effect the damage he can do with his sword.

No skill is an island. Having a skill with one thing could affect other skills a character also has. Or maybe even skills they don’t have. A fitness skill would affect a foot speed skill, especially at longer distances. Proficiency with a staff could provide implied proficiency with improvised weapons like branches. Skills with plants and herbs can affect a first aid skill. A skill in weaponsmithing could allow the character to be at least degree one proficient with any weapon he would have smithed often. A skill with woodcarving could allow a character to carve a crude bow or arrows in a pinch, even if they aren’t really a bowyer or fletcher by trade.

But a word of warning. Just because a GM could make a complex system of skills interacting with other skills doesn’t mean they should. Most of this should be decided on the fly, especially as it usually just allows another two dice per degree of the skill or otherwise increases the duration, area of effect, or distance of the skill being augmented. A complex system of skills can make for a tedious character creation process and defeats the purpose of making this system easy for anyone to pick up and use. Keep it simple. But have fun too.