One thing which I do is keep some form of cardio in all year round. HIIT or steady state fasted cardio. There are MULTIPLE benefits to this one of the obvious benefits is a more active metabolism. If I am at a phase where I am either happy with my body and want to maintain it I’d usually keep it to 20-30 minutes 3-4 times a week. When trying to put on weight I only do it 2 times a week.
This will depend largely on your body composition and if you lean enough and your current calorie intake Vs. your calorie expenditure. However, including “high days” is going to potentially have many benefits including adding fuel to the fire, that is your metabolism. This will usually mean a higher carb day, which will directly stimulate your thyroid output.
So there are a LOT of natural thermogenic stimulants which can boost your metabolic rate. I am not a big user of fat burners, but IF you do use them then only use them for short bursts. If you become over reliant on them then that is exactly what will happen to your body, it will become unresponsive and ultimately make it more difficult to shift body fat.
Keep your calories high
Along with cardio this is the simplest form of boosting your metabolic rate! In MANY cases I find people can eat more whilst NOT gaining anymore body fat. They can in theory elevate their calorie ceiling without any negative effects, in fact there’s only benefits . An easy, no risk way of doing this is to increase your calories by around 10-20% of your current intake. Monitor your waistline and body composition, if you not increasing body fat or weight increase the weight again in couple weeks. it’s the easiest, simplest way of boosting your metabolism