1. How to get more vivid dreams?
Eating things with melatonin like cherries helps. A good diet can aid in this. However, largely you just need a good quality of sleep.
2. Which is the best technique for getting lucid?
There isn't one way that is the best. The easiest is DEILD. Set an alarm to wake you up 6 hours after you go to bed. When that alarm goes off, switch it off, go back to bed and get comfortable, then try not to move and tell yourself "I am lucid" over and over until you get tired.
3. What are Sleep Paralysis hallucinations like?
Just ignore it altogether, I for one rarely experience SP anymore. Its not scary unless you make it scary.
4. Are WILD drams more vivid then others?
In my experience yes, but thats probably because you are highly conscious the moment you enter the dream, where with the DILD method you have been in a dream-like frame of mind for a long time and its easier to lose lucidity.