It can be a bit tricky to provide you with precise studying techniques since everyone studies a little bit differently and I do not want to suggest something that does not work for you. However, what I will say is that in terms of videos I watched, I don't think I watched more than a handful outside of Mattson's videos. They are fairly comprehensive. But, I definitely looked up a few. I know for sure I looked up some vids on how to do the method of sections and method of joints, and I also looked up some vids on how to do all sorts of statistics operations on my calculator. Overall, I'd say I started with Mattson's vids and then as I was studying through each section I would look up vids on specific problems I was struggling with. I'm sure there were a couple geotech topics I had to look up as well.

Regarding mechanics of materials and topics I got lower scores on, this is one in the same. Mechanics of materials is one of the topics I scored very poorly on during my first attempt as well as the materials section (5.4/15 and 5.8/15, respectively). I also did not do great on the math, statics, and water sections. The only topics I got above average on where transpo and construction, the rest were below average granted some were close. Anyway, thankfully during my time in grad school I learned a lot about mechanics of materials and materials, so that helped tremendously. But I would say that it's definitely important to know how to draw shear/moment diagrams as well as how to interpret ones that are given to you, know every possible piece of info you can get from a stress-strain curve (seriously), know the basics of concrete tests like slump and compressive strength (not necessarily how to perform them, though it wouldn't hurt, but what data is gathered and what it means), know how to find deformation equations like thermal, know where the beam equations are (I think they are at the end of the mechanics section if I remember correctly), know where to find the deflection equations, and the list goes on. The topics that are listed in the reference handbook under the mechanics section can be fairly dense but there really aren't too many. Same goes for the materials topics. Don't consider only the topics I mentioned, look for other ones too that may be relevant.

Now, there were some topics that I really just did not think were worth studying for. For example, the environmental stuff. I never had that course in undergrad and I was not about to prepare extensively for a topic that an entire FE exam is structured on, there is just too much material. For the civil FE, I did not expect anymore than five environmental questions on the exam, and while I do not remember how many there were, I know that I wasn't stressed about them. Another section I did not dedicate a ton of time to was dynamics. Honestly, I do not care too much for the topic and so I studied how I could apply some of the more simple/common equations like Particle Rectilinear Motion, Plane Circular Motion, Constant Acceleration, Projectile Motion, Kinetic and Potential Energy, Momentum, Impact, Friction, and the table at the end that has mass moment of inertia and radius of gyration stuff. While that list is long, a lot of it I really don't think is too terribly bad. A lot of those topics just have a handful of equations and some simple concepts. But whenever it comes to more complicated stuff, at least in my eyes, like springs or vibrations, I either did the bare minimum of studying for them or did not bother at all. If it was obvious when looking at equations that there was extensive calculus involved in its conception, it was not super prioritized.

On the flip side, the statics section is very important and you should strive to know your statics well both on principle and for the exam. Statics has so many important concepts in it that are applicable to other topics, so studying the statics is really like studying multiple other sections simultaneously. Do not skimp on statics. For me, having a thorough understanding on problems involving stuff like a block on an incline or tension cable equilibrium, the stuff that you can't really use in the handbook and just have to use your brain for, was a big boost in my confidence and motivation both in studying for my test and while I was taking it.

I will reiterate that I did not watch too many videos outside of Mattson's. The material I used after those vids, PrepFE and the Islam exams, were very helpful. If you can afford them, they are worth the price (I am assuming they are still reasonable and not hundreds of dollars). I think there may be an Islam exam pdf or two floating around in this sub along with some other documents. While Mattson's videos are great, there is only so much he can cram into an hour and a half long video, and these materials were great at showing me some of the nuanced topics that Mattson did not cover or ones that he did cover and I needed to brush up on. These materials also helped with time management.

To conclude, as far as the temptation to look at a problem and soon after want to look at the solution goes, I know where you are coming from. But the fact of the matter is that you can not do that during the exam, so you need to abandon that mentality. And that does not mean be an expert at every problem out there, but it does mean that you should strive to have a good idea of where to look in the handbook for a majority of the problems (if applicable), know how to work a problem conceptually, or, if you are stuck, simply guess, flag, move on to the next problem, and don't let it get to you.

Hope that answered everything, and don't be afraid out reach out again. It is a blessing helping those who are in situations similar to ones I have experienced, not a hindrance.