did you try following along with a book, and echoing every prayer of the priest and deacons in your heart, and also adding your own prayers or repentance during the silent parts? or during the Bible reading, you can follow along in your Bible to make sure you don't miss anything. work out how you are going to apply the words in your life the following week and make a mental list of any questions to ask the priest or deacons at the end.
think of the people who need your prayer and pray for them during the service. join in the hymns and chants and make the words your words. pray for the priest and the deacons. pray for the old lady in front of you and the annoying loud children behind you.
if you've done all that and you're still only half way through the service, then meditate on Jesus great sacrifice for us, and the wonder of creation. look around the church at the icons, how many of the saints stories do you know? which ones inspire you and why?
look around and think if any service is needed in the church. can you collect the offering? are there enough people to make tea? would they like a break?
after all these thoughts, prayers and meditations, you might actually forget when the service is going to end, so make sure you don't miss anything, like giving the offering or taking Holy Communion. and if you are still praying when the service has ended, feel free to stay a while with God, finishing your prayers.
and if you benefitted from the service after this, be sure to tell someone this and ask what they thought. maybe they have the same problem as you, so you can give them advice, or maybe they will have ideas much better than my own on how to concentrate during the liturgy