Psalm 88
This psalm is full of lamentation over trouble and tribulation and the writer is pleading with God for mercy. Sometimes as Believers we are severely tested with the worst of inward troubles and are distracted with dispair.  Praise God we can approach the Throne of grace for mercy and strength.

Psalm 91
Oh, what wonderful promises in this psalm. There is the promise of preservation of those whose confidence is in the Lord. Those who live a life of communion with God are constantly safe under His protecting wing. He will be their rest and refuge forever.  The writer records in Psalm 91 a prophecy of the wrath of God and what will happen to believers. They understood this promise from the Lord concerning believers during the wrath of God.
"He will cover you with his feathers."
Jesus promised the same thing.
Mat 23:37
"Jerusalem, Jerusalem, you kill the prophets and stone to death those sent to you! How often I wanted to gather your children together the way a hen gathers her chicks under her wings! But you were not willing!

For he will command his angels concerning you to guard you in all your ways; they will lift you up in their hands...
He has promised us that He will take care of us in the matter of spiritual things but often in the matter of physical things too.  

Psalm 95
We should sing His praises out of the abundance of a heart filled with love, joy and thankfulness.  There are many references in the book of Hebrews to this passage.

Psalm 108
We should praise God publicly as those who are not ashamed of  Him and desire that others also may be affected with a realization of His goodness and the value of leaning upon His promises.

Psalm 109
David offers this admonition.
“He wore cursing as his garment; it entered into his body like water, into his bones like oil.”
Cursing and related sins come easily and freely. Cursing becomes familiar the more we use it. It slips out at inappropriate times. It’s “usage familiarity”.

Compare “cursing as his garment” with our “garments of salvation”. (Isa 61:10)

May we be reminded of our “garments of salvation” when “usage familiarity” causes cursing to slip out. Remember we can't "unsay" anything.