ssd – What's the easiest way to clone a boot partition?

At the present time, I use a 1 TB hard drive for Ubuntu 18.10, but the used space is only 50 GB (only one partition). I'm looking to buy a 250 GB SSD and install 18.10 but I do not want to install clean, because it will take time for everything to be adjusted as I wish.

I am now reducing the partition from 1TB to 100GB because, as I read on the Internet, we can not clone a partition larger than the destination drive / partition. So, what is the easiest way to do it? I've read about Clonezilla, but there's only one tutorial for cloning drive-to-drive, no partition to partition.

Please help me, thank you 🙂