I've received many calls over the years from people asking how to keep certain birds away from their feeder.   This in a hard problem to solve, but let me give you some suggestions.   First, if the birds you want to keep away are large birds such as Doves, Blackbirds, Grackles, etc. just make the perches on your tube feeders too short for them to stand on.  If you are using platform feeders, switch to tube feeders.   If you are talking about a type of smaller birds, you are in trouble.   You usually can't keep one type of small bird away without keeping them all away.  However, different birds like different feeds, so proper selections of feeds will help, but not completely solve this problem because the birds are very adaptable over time.

I get a lot of calls on Grackles living in the walls and attic of people's homes.   These birds will move into any opening they can find in your house.   And will, if necessary enlarge the opening in order to use it, provided the material is soft enough for them to do this.   The best advice is to make sure you have every opening sealed.  Fall is the best time to seal these opening since the birds are not using them. 

Every spring I hear about birds flying into windows.   They do this because they see their reflection and think it is another male trying to move into their territory.   Many species of birds are very territorial and will fight with any male of the same species that entersa their area, especially just before and during their mating season.   The only way to stop this behavior is to eliminate the reflection or scare the bird away.   White paper taped in the window will stop the reflection many times.    A silhouette of a hawk taped in the window will often scare the bird away.