For basic blocking, i would go into the sp tutorial and just try and block, dont attack back. 10 minutes a day of that will help you improve.
Play native siege/deathmatch and just practice blocking there too.
Duel servers will be too hard unless you can find someone of the same skill level, or who wants to help.
As for attacking effectively. I'm not one of the greats, but I think knowing about speed bonus/glancing helps a lot.
Judging weapon range is something i do a lot. I don't even try and block if I'm doing that, and sometimes I get it wrong and die.
Try and take control of the fight, if people are backing away from you, they are making you move towards them and if their weapon outranges you, you're not going to have the advantage.
Mixing things up, changing attacks/holds etc can help, changing the pace of the fight a few times if it's a good player.