In order to intensify the quality of an adjective or adverb,
we use muy:
Estoy muy cansado – I am very tired
If you want to soften it, use un poco:
Estoy un poco cansado – I am a little bit tired
In order to intensify an abstract noun, you may use mucho + masculine or mucha + femenine. To soften it, use un poco de:
Tengo mucha hambre – I am very hungry
Tengo un poco de hambre – I am a little bit hungry
Usually with estar you will use muy, un poco, and with tener, mucho, un poco de.
The word bastante can be used with both nouns and adjectives, and it means enough or quite:
Estoy bastante cansado – I am quite tired
Tienen bastante trabajo – They have enough work
Words mucho, mucha and bastante agree with nouns in number:
Juan tiene muchos
coches – Juan has a lot of cars
Juan tiene bastantes coches – Juan has enough cars
With adjectives bastante doesn´t change:
Juan y Luis están bastante__ tristes – Juan and Luis are quite sad