Don’t clone! Instead use your current TimeMachine backup or your copy off your stuff from your HDD to your new SSD via Migration Assistant! So here’s the details:
Setup a USB thumb drive as a bootable OS installer How to create a bootable macOS Sierra installer drive I do recommend sticking with Sierra on the older MacBook Pro’s with SATA drives, HFS+ is better than APFS! On them. I don’t recommend High Sierra instead you’ll want to jump to Mojave but Apple doesn’t support it on this series you’ll need to use a hack to installed from DOS Dude1.
Get a StarTech 2.5" SATA to USB adapter cable (or something like it) so you can copy off your stuff from your current HDD.
Get a new MacBook Pro 13" Unibody (Mid 2012) Hard Drive Cable and yes! This it’s the one thats for the 2012 model as its better! Your current cable is not able to support the I/O data flow your new SSD can push and oftentimes the cable is worn as well.
You’ll want to follow this IFIXIT guide in replacing the cable MacBook Pro 13" Unibody 中期2012 硬盘线缆替换 and in addition add a strip of electricians tape on the uppercase where the cable crosses over to help protect it from the rough surface of the uppercase. And lastly very important! Don’t crease the cable! The sharp folds damage the thin foil wires inside, you want nice smooth arcs around the bends and corners. At this time take your old drive out and put the new one in.
With your USB installer format and install your OS onto your SSD
And lastly, plug in your old HDD via the SATA to USB cable and run Migration Assistant How to transfer your old Mac's data to your new Mac