Yep, what Maylar says.
Many of us have the same issue and a bit of trial and error is needed. However, there are some things that you can do to improve your blend for cider. If your cider is lacking in acid (i.e. it is a bit "flabby"), adding Malic Acid to bring the Total Acidity up to between 5g/L and 7g/L will make a big difference. You can measure the TA with a test kit available from most brewing suppliers. Be aware that these kits are usually intended for wine where the major acid is Tartaric, whereas cider has mostly Malic Acid so the test kit results need to be multiplied by 0.89 to convert to Malic.
Most eating apples have a TA in the order of 3g/L whereas some cooking varieties such as Granny Smith can have a TA of 10g/L so If you know what you have it will give you a guide to blending.
Ideally your cider should have a pH of 3.8 or below in order to protect it from pathogens until the alcohol level builds up. Adding acid helps with this since many eating apples have a pH of 4.0 or higher
As far as tannin is concerned, there are also a few "tricks". Adding black tea (made with boiling water to sterilise it) works as does adding oak chips etc. I have used tannin powder successfully and have recently tried adding red apple peel (this has higher concentration of tannin than the flesh) to primary fermentation.
There are some excellent papers on this subject by Micah Martin and others published by Cornell University (googling "tannin, cider, Martin, Cornell University" should find them for you.
Hope this helps.