So I do WBTB after like 4hs and when I wake up and do MILD, it's really hard for me to fall asleep. One thing could be the blinders in my room don't work and let light it. My mind is really active and I also get up to use the bathroom. So I was wondering, any ways or tips to deal with this?
You will improve with practice. As for your blinds, maybe just buy blinds that work? Or a sleep mask. When you wake up, try not to think of anything, except for lucid dreaming if you're going to do a MILD. Eg if you wake up to do FILD then just think about finger movements, not the dream yet. If you're going to do WILD that's different.
I use a black out curtain and blinds. I repeat in my mind a very simple phrase or I count my breaths for just a few then start over. The idea is that you will not be able to think random thoughts if you force a short phrase or numbers into the quiet space. If you find you have stopped and are thinking, do not judge or be frustrated, just go back to doing it.