Sometimes I have problems focusing--on the Lord while I'm trying to pray or study the Word, on my children when I have other things to do, on a friend while talking on the phone, or on a task I'm trying to complete at home.
Here are some solutions that work for me:
Make a list--It helps me to dump out my thoughts and get them on paper so that they don't plague me throughout the day. The list might be packing for an upcoming trip, things to do for the week, groceries, calls I need to make that day or anything that is frequenting my thoughts. I even keep my planner or a piece of paper next to me while praying. It is certainly less than ideal to interrupt my time with God to write on a list, but I find that I can stay focused if I take a few seconds to jot something down, and then return.
Turn it off--If the computer, the TV, and/or the radio are on, I experience overload, especially if I'm trying to listen to my husband talk about his day, or to my kids, or talking on the phone. The same can go for the phone. Just because it rings, doesn't mean you have to answer it.
Do One Thing--This works for listening, but also in doing tasks at home. I should be able to fold laundry while I'm watching TV, but sometimes it's easier to do it quickly and single-mindedly by not multi-tasking by talking on the phone or watching TV while I'm doing it. The same goes for the phone--just because it rings, doesn't mean you have to answer it if you are completing a task or giving a family member your attention.
I certainly don't go to these extreme levels all the time, but if I'm having trouble getting something done, or giving someone the attention they need and deserve, it seems to help.