It should be in everyone's interest to look to gain muscle. It contributes to metabolism. An increased level of metabolism will make it easier to keep fat off. Not only this, but muscle will help keep a good posture, increase longevity, make functioning on a day to day basis easier and a plethora of other positive outcomes.
Here are some basic, straight forward points to make sure you are going in the right direction.
1. Consume enough protein to support muscle growth and don't be in too much of a calorie deficit.
Generally speaking, consuming 2g of protein per kg of bodyweight should be sufficient for the average person. For example, an 80kg person would look to take on 160g of protein. You may hear of bodybuilders consuming way more than that. From what I understand, the necessity for that is just not there for your average person. Use this as number as a base guideline and build around it. I would suggest for you to try things out for yourself. You'll learn what works for you, what doesn't work for you. If you find you aren't building much muscle, try changing up your macros and see what effect that might have on your performance and appearance. What works for one person won't necessarily work for another. Track progress so that you can see and measure what might be working for you and what might not be working. Make sure your total calorie intake is not too low. If you are on a massive deficit, it will be very hard for your body to repair and grow muscle.
2. Lift weights.
I know this is a bit of a no shit sherlock, but it's needed to be said. Just because you run doesn't mean your legs are strong, you need to get some resistance work in too. Lifting weights is key. This can get way more complicated but, if you are completely new to lifting, then keep it simple. Make sure you complete a whole body workout. Keep it to roughly an hour. Make sure the last rep per set is difficult. Do your workout about 3x a week and you should have a pretty sweet starting point. If you don't want to go to a gym, then you can lift weights at home. You can of course use bodyweight/resistance band/kettlebell etc exercises too, it doesn't matter the modality so long as you are using some sort of resistance.
3. Be consistent.
Don't keep switching back and forth between different workouts too often. Try to run some sort of a programme of weights for a minimum of 8 weeks, especially if you are starting out new. For more advanced lifters, they might be able to switch a bit more frequently with their programming, like every 4-6 weeks. Don't start one particular programme, give up on it, then move on, the body hasn't had time to adapt. Muscle confusion is a thing, utilise it, but don't over utilise it. Allow adaptations to be put in place, allow progression in weights, allow movements and co-ordination to improve, then look to move on before you plateau and chase those gains. Be consistent in terms of getting to the gym too, get there 3x a week as often as possible. A week off because you're ill is acceptable. A week off because you missed the first workout day is not.
Bonus gains!
Recover!! If you are having poor sleep, whether that be the quality of the sleep, or lack of sleep, or both, this is going to affect your results in the gym poorly. I'm sure you've heard this before, "recovery is as important as the workout itself". To make sure your sleep is on point, you can do some of the following things:
1. Have good sleep hygiene.
No, I don't mean brushing your teeth in your sleep. Have a good routine before you get yourself into bed and keep that routine the same. Try to go to sleep and wake up similar times every day. Try to keep off technology around an hour before getting into bed. Use blue light filters if you do use technology (whether these help or not, the Jury's out, but no harm in using them none-the-less). I use this one for my windows laptop. Have a google for a mac one. iPhones now tend to have blue light filters if you have an iPhone 5 SE or beyond that generation. Make sure you spend most of the time in your bedroom asleep so that your body associates that room with sleeping. All these things will help you have good sleep hygiene. There are many other points that can be made.
2. Magnesium supplementation.
If you still find your sleep quality is poor, supplementing with magnesium can help. Try to make sure that the form of magnesium you are taking is bioavailable. Take it on an empty stomach an hour before getting into bed.
3. Avoid late consumption of caffeine.
This is going to be very individually-based. But, if you find you're having poor sleep, or getting to sleep is difficult, and you're having 12 cups of coffee, then perhaps cutting back on all those coffees could help you sleep. For me personally, I'm one of those weirdos who doesn't really drink coffee often. When I do, I feel like I'm very sensitive to the caffeine and I'm buzzed not too long after. Because of that, I tend to avoid having coffee too late in the afternoon.
Good luck and thanks for reading!
BennyFit