I’m a new player and wondering whether I should be spending skill points into my mastery bar or improving skills as I level.
A rough guideline to follow that’s not half bad is 2 points into your mastery bar and 1 into skills. Most of the time, you don’t need to max a skill or modifier for it to do well early on, the important part though is to not neglect your mastery bar as it provides core stats that help you survive.
That said though, the more you play and learn, you’ll find that some skills or modifiers can be maxed ASAP for effectively free damage at little-to-no gain (such as energy cost). Examples are Lethal Assault/Deadly Momentum, Lightning Tether or pets like the Familiar/Briarthorn.
Edit: Forgot to say but welcome to the game! 
Welcome to the forum!
I personally use one skill offensively,which I maxed.Also some defensive skills and few one point wonders.Everything else is in mastery.Especially if I need the exclusive skill at the end of the class tree.Inquisitor,rush to get Censure around level 30.Or acid Sentinel,I need Celestial presence and Path of tree.
Also is important to noticed,if you’re falling behind in health/defensive ability or offensive ability.If you do,putting more points in mastery bar can be cheap solution for the problem.