When you stand in front of a creep he will try to pass on your left/right side,so you need to adequately move slightly left/right to block him from passing around you.As long as you keep blocking the first creep on the head of the wave,the creeps that follow will block each other.And avoid scattering the wave(with spells,other heroes,courier...) since creeps that are further away from group will have different pathfinding and could pass you from weird directions.
It is best to start blocking near your Tier 2 tower,since at that point your creeps will be nicely lined up.
If you have another teammate in the lane it is best that one blocks the creeps and other one stays further in front of the group.So if a creep bypasses you,your teammate will be there ready to block him,while you go ahead in case creep passes him too.
Blocking gets easier with larger heroes(pudge,lucifer...) since you have to maneuver less,and if hero is slower you will less likely move too far on the sides which could make the creep pass by you and ruin the block.
Pulling you can attack the neutral creeps(side lanes) and lead them close to your creeps on lane making them fight behind your tower and delaying the creeps progress.
Since patch 6.79 creeps in the safe lane have a bonus movement speed for few seconds when they initially spawn,making them harder to block.Watch for more details.
Hero Skills (this is prohibited by some tournament rules)
Earthshaker can use "fissure" on certain places and completely block the creeps from progressing(for the
duration).
Furion can use "sprout" to trap the creeps(if you manage to group them enough).
Clockwerk can use "cogs" to trap the creeps(if you manage to group them enough).
Videos
Take care that Dota 2 traffic is not the only thing you should take into account. There are weekly Dota 2 patches (200-500MB), there are Steam patches and Steam traffic.
But speaking about Dota 2 client traffic only, I just measured a single match of 40 minutes and here are the results:
- around 37 MB downloaded
- around 11 MB uploaded
Best Answer
According to this website: http://dota2.gamepedia.com/Diffusal_Blade
The movespeed slows 100%, and then the slow decreases in 0.8 second intervals, so it slows for 100%/80%/60%/40%/20%, going one step down every 0.8 seconds.
This page also has some info on the buff: PURGE http://dota2.gamepedia.com/Purge
As for the slow stack, I believe it does but I don't think you can slow a hero beyond 100%. That means, once the slow goes 80% or lower then you can see the effects of the other stacked slow items.