Hey guys,
I have canon XHA1 Camera and I use Adobe Premiere for my editing.
What is the best way to do slowmotion on my video ?
Now I just use Speed / Duration and change it from 100% to 80%
But I don't know if this is a good solution and if there are better ways to do it.
Maybe via plugins or just use the Time Remapping in AE.

plenty of threads on this topic. You are doing it correctly. Just be sure to turn "Frame Blending" off when changing a clips speed. Magic Bullet also has great reviews.

JS

AE using time-stretch and "pixel motion" frame blending.

this was shot at PAL SD:
Knighthood footage fullspeed on Vimeo (http://www.vimeo.com/4948545)

...then slowed to 1/16th speed.
Knighthood footage, roto'ed v2 on Vimeo (http://www.vimeo.com/5035441)

...and here it is at 1/64th:
Knighthood footage 64th speed on Vimeo (http://www.vimeo.com/4948598)

-drew

If you're looking for a simple 50% speed, PP's Time Remapping feature works really well. I have mixed feelings on frame blending. Sometimes having it on can improve the look, at least to my eyes. The rest of the time it just spews. A little test both ways on your footage is probably the best option. The good thing about this workflow is that you never have to leave Premier.

If you want something something that really kicks for something fancy, After Effects Time Warp has plenty of options. Make sure that you don't use the frame blending option. Use Pixel Motion instead. It's wicked CPU intensive in rendering and can lose its mind sometimes when trying to figure out where to move the pixels. You might have to fiddle with the settings a bit to get what you want.

Twixtor is a good solution also...