As a chronic worrier, I often find myself losing perspective on what I am actually doing, or how I am actually going. The paragraphs below are mainly written for my benefit. It may benefit you too.
One of the remarkable things about ministry of the Word is God's supervision over it. And the Word of God brings about "successful" ministry in its own right. For, just as
the rain and the snow come down from heaven
and do not return there but water the earth,
making it bring forth and sprout,
giving seed to the sower and bread to the eater,
so shall my word be that goes out from my mouth;
it shall not return to me empty,
but it shall accomplish that which I purpose,
and shall succeed in the thing for which I sent it. Isaiah 55:10-11
So, if we are faithful in proclaiming the Word of God, then our ministry is "successful". For success must be defined in terms of God's purposes, regardless of what we or the world perceives success to be. We may not see any fruit, any change in the people to whom we minister, but we must trust God that his purposes has been and will be fulfilled.
This is very liberating. The success of God's work is quite independent of our feeble efforts.
The hard bit, of course, is being faithful.
One final quote:
All of us who engage in preaching or speaking about Jesus must be aware of this situation [that Jesus has received all authority and dominion], and aware that we are doing it in the context of that authority. God's word will not lack power so long as it is a true word from him... We ourselves are weak, but the power of Christ through the word of God is irresistible. We should always be conscious of this situation as we evangelize, for this consciousness will save us from desperate and unworthy methods, or from despondency, or from false hope or from human timetables. D. Broughton Knox, Protestant Faith radio broadcast, 23 June 1974