Honestly, the best suggestion is to not play one. You waste invocations and feats just trying to break even with your bog standard agonizing eldritch blast. Pact of the Blade/Hexblade are basically trap options. If they got the extra attack invocation for free it might balance better, but you just keep having to throw more and more build options to try and keep up, while the EB warlock is getting to expand their versatility and increase their power. Granted, 5E is kind of easy mode, so pretty much anyone can function, but its decidedly less effective.
