In that case I would recommend the following:
1. Improvisation generally works best if you have a half decent understanding of and familiarity with scales. For Blues and early Rock, the minor pentatonic would be a good place to start. Some would doubtless recommend the Blues scale but in truth you don't really need it as you can simply add blue notes into your pentatonic scale as your skill develops. In learning scales, don't forget that the reason you're learning them is so that you can play music. I haven't taught for some years so I'm a bit out of touch, but you can get Blues backing tracks as freebies off the internet - I've just had a quick look on Youtube and there's loads of 'em. Metronomes are ok for building speed and accuracy into your scales, but not recommended for playing actual music IME. As time passes and your technique develops you can start looking at other scale types; Major scale and some of it's modes would be a good place to go next. You may develop an interest in Jazz improvisation, but fair warning, that's another ballgame entirely.
2. Depending on your preferred playing style it might be a good idea to start looking at some fretting-hand techniques: slides, hammers, pulls and string bending are all important tools for Blues and Rock improvisation. Again, there's plenty of guidance around the net.
3. Whilst it is possible to pick up standard licks, trying to learn them in isolation is definitely doing it the hard way. You'll have a better chance of learning them effectively if you've spent some time developing the techniques needed to play them
4. If you can afford it, try to get some lessons from a good teacher. Yes it's an expensive way to do it, but you'll get the benefit of a structured approach and expert guidance. Getting things right the first time is a lot less painful than having to sort bad habits ten years down the line. Your money your choice of course, but just so I've said it.
5. Don't expect to be reeling off classy Blues licks in a couple of weeks; improvisational skill takes time, practice, perseverence and patience. Learn how to manage your expectations. You will get bad days, so be prepared for them and don't let them put you off. Worst case scenario, you can always put the guitar down and come back to it tomorrow.