Doubles Defence

Can you please describe the first 2-3 difficulties in your games applying your practice? A few things come to mind.

 

That looks fine. You're covering the basics of the different types of defense, so that's good.
Would you mind recording yourself and posting the video here so we can give more targeted advice?

So you mean you're trying to defend short / drive, and don't have a good height / length?

The first step would be to learn the high clear defense - sending the shuttle high and deep. This will keep you out of the biggest trouble, even though you won't be able to take the attack back.
Once you know how to do this, learn the short defense (low defense going behind the net).
The drive is more tricky to do, since you can't do it on any smash, and failing to do it properly is usually severely punished

 

My advice is keep your body low and make your body face the direction of the smasher.

 

When you recognize your opponent's smash is fast(er)/harder(er) than what you practice, try to block it back away from the front opponent. This usually requires minimal hand swing, and thus making it best for this situation. Make sure you're not too tense, both in your mind and your hand/arm.

If you always do straight block (or "stop"), opponent could recognize and anticipate them.

 

I am a singles player so when i play doubles, i have no problem blocking a smash. I feel quite comfortable driving back a smash but i really suck at doing the high clear defence. Unless the smash is really slow then i can take my time and clear it back. But when i play with better players and they have a really decent smash, I cant really clear it back to the baseline and it gets worse when they smash my forehand.