The built in glass shader is pretty much a refraction/glossy/fresnel[factor] into a mix node combo. It is pretty accurate, but if you need to exaggerate effects or have better control over it, you should just build your own using mentioned nodes. For common glass, reflectance at facing angle should be around 4% (about that for all dielectric materials), in case you want to control it differently.
If faking glass, using a transparency shader instead of a refraction one, you can’t use fresnel. Get some background info from this PBR in Cycles tutorial: https://www.youtube.com/watch?v=WU0bmUkkiyA (just replace Diffuse with Refraction/Transparency).