Experience is generally the best teacher for what lenses you need. Buying lenses on a whim or someone somewhere recommends this or that, you'll end up spending more money than you want and ultimately have lenses that spend most of their time in your camera bag. This I know...as in 'been there, done that'.
Perhaps it was GAS (Gear Acquisition Syndrome) or plain old greed, but I ended up with 6 L lenses and an EF 85 f1.8 - for portraits. My basic plan was overlapping-range zoom lenses and 3 primes for their outstanding clarity. I fortunately sold one of the L zooms 3 months after buying it as it's range was fully covered by my other zooms. 15 months later, I unloaded the 200 f2.8L and 85 f1.8 due to lack of use. I think I took less than 100 frames with the 2 of them, combined!
Bottom line, what do you need? Fast lenses for low light work? A long tele for birding? What do you shoot mostly? That's where to start. What works for me may work for you, maybe not. At present, I have 3 overlapping range zooms covering everything from 16mm to 200mm, and the 135L for it's jaw dropping results. Of the 4, the 24-105 f4L is mounted for perhaps 60-70% of all my shots.