The benefit from overclocking will primarily be in cases where the CPU is the bottleneck. However, for most games at the moment your GPU is the bottleneck and so the only way to improve your gaming performance is to get a better GPU. That being said, it might be more cost effective to get a new system entirely.
As far as trying to get more performance without spending money (or spending very little), you have very few options. You have to understand, you have parts that would've been considered low to mid range when they were new. They are now almost 7 years old. That is a really long time to expect budget components to be viable. Consider that the 750 Ti, which is what is considered to be the minimum needed for a decent 1080p experience, is about 30x more powerful as the card you have, and the recommended card for budget 1080p builds (the 1050 Ti) is a little short of 50x as powerful. Your CPU is less of a problem, and only approx 1/2 as powerful (after you OC it) as the current recommended budget CPU (i3-6100), but you see where I'm going with this. Unfortunately, there comes a point when there's not much you can do other than buying a new machine. Technology evolves, and in the case of GPUs has been evolving very rapidly, and your expensive machines become obsolete. You can try OCing your CPU, RAM, GPU, and tweaking all manners of settings, but while it will be a fun exercise, it won't give you noticeable improvement in semi-modern games and it won't really bring your computer to meet the min spec for the latest games.