Joseph Smith:
"I do not dwell upon your faults, and you shall not upon mine. Charity, which is love, covereth a multitude of sins, and I have often covered up all the faults among you; but the prettiest thing is to have no faults at all. We should cultivate a meek, quiet, and peaceable spirit" - History of the Church 5:517
Wilford Woodruff:
"Brethren and sisters, you should live by faith, realizing every day that all power rests with God, and that it is through him that we are able to live in peace and enjoy plenty." - The Discourses of Wilford Woodruff, pg 222
And I know you're looking for quotes from modern prophets... But I'm going to break that rule right off the bat
Because I was trying to apply this principle to my life once and was greatly blessed for my efforts... But it's so much easier to not follow these simple principles; so it's my new year's resolution
2 Peter 1:
4 Whereby are given unto us exceeding great and precious promises: that by these ye might be partakers of the divine nature, having escaped the corruption that is in the world through lust.
5 And beside this, giving all diligence, add to your faith virtue; and to virtue knowledge;
6 And to knowledge temperance; and to temperance patience; and to patience godliness;
7 And to godliness brotherly kindness; and to brotherly kindness charity.
8 For if these things be in you, and abound, they make you that ye shall neither be barren nor unfruitful in the knowledge of our Lord Jesus Christ.