Dont forget, I have almost 10 years back training. I have never been a lean individual. It is only the last 4-5 years that I have found my way in that regard.
I am lucky to respond well to training, and building strength as size have never been an issue for me. I went from 140 to 190lbs in 3 years from 18-21. I still have giant zipper stretch marks all over. I just blew up after finally hitting the weights. I am lucky I guess, that I am built to generate reasonable power with no real strong or weak points. I am not really great at any one lift and not really bad either. Some guys are freaks at one thing and have relatively weak lifts in comparison. I am fairly well balanced.
Depending on your length of training, and current condition, there are several ways to approach your training. It is also important to understand just what it is you want and how dedicated you are willing to be to get it. There is nothing wrong with just training, and making aprox efforts on diet and letting time do it's thing.
In contrast, if you want the most efficient training possible with the fastest results, you have to start putting your nutrition as important or moreso than training. (it certainly takes A LOT more work do eat right than just showing up to the gym 4 days a week).
The advice I would give is based a lot on the above...and again, there are no 'wrong' answers. It has to work for your goals and how much effort you really want to put forward.
We all start somewhere. I was out of the gym for a decade. This is what I looked like.

Dropping weight was my first goal.

Then this is my first year back training after dropping weight. I think I was 178 in left pic and 195 after a year of training. This is only possible because I was the same basic size in my 20's so I only had to bring it back. Much easier to come back than gain the first time around.

Consistency over time will yield results. Most people's lack of results is because they dont manipulate their food. If gaining mass and strength is your goal (assuming you still have progress you can make), and you stay the same weight more than 2 weeks in a row, you are NOT doing things in the most efficient manner. FOOD, both deficit and surplus is the key to linear success.
I spent almost 5 years eating up for 5 months and then dieting for 2 1/2-3. In the course of gaining, I gained and lost HUNDREDS of lbs. I would eat up 25-30 lbs, and the diet right back down. Each time holding on to what I could.
Anyway.. I dont eat up and down anymore, because there really is no gaining for me anymore. I dont really want to use anabolics at a level that would be necessary for me to get bigger so I am happy where I am just being healthy. I would never want to get any bigger than I could maintain on natural test levels. I also dont think I could handle losing strength.
So I work on keeping good composition and just staying 'fit' these days. I am fairly happy but I miss the days of really working hard in the gym. Being able to reach new goals and compete with oneself is incredibly motivating. I satisfy that with helping others achieve from time to time.
I dont know it all, but I have a pretty decent handle on things. Remember, I was NEVER a lean person, but after years of heavy training, I finally decided to shed some fat and I was shocked that I didnt look all that bad underneath (even though I have never been a "bodybuilder".
