@Gimlisk,
As Adoede mentioned, you get 100 skill points to use for your build, and each rank you increase a skill significantly improves its effectiveness. Most managers of successful glads run them with 10 skills at rank 10, with a small minority that are running 11 skills (9 at 10 and 2 at 5). It greatly helps if you plan out your build from the start and know where you may want to go. Of course, that may change and evolve, but you should have a good idea for the core or chassis of your build. Make sure you read through the skill trees and understand how it works, and what the prerequisites are to obtain a particular skill (some are class specific, some require a certain number of points already invested in prior class skills). If you check in each of the class forums, you'll find a stickied thread that discusses on "how to make a xyz" where the skills are discussed.
Regarding your inactivity, again Adoede brought up some great points. Also bear in mind what your encumbrance and strategy is. If you are >50% encumbrance, you will be slow on the sands. If you're running all trugs or dunder, they have low initiative. If you're fighting superior glads, you may just be getting overwhelmed. It's also tough because at those mid brackets, some glads are further developed than others.
If you can post your glad race, attributes, skills, equipment, and fight strategy we can offer a little more focussed advice.
Passive skills are ones that are always "on". You don't see them trigger because the effect is always present.