Well few days back i purchased this lowcast , high speed phone with dual sim support,
being techie my concern in only performance of the device not the design,and this phone performs really well , better than Samsung phones, battery life is simply awesome, more than 24 hours

ImageTaken From Sonymobile.com

but i was facing a problem from the day 1, and it was weak signal strength on sim1, i thought may be its a low network coverage on place where i work , but i realized all other colleagues were getting full signals on their phones,

so this is how solved my problem in 5 simple steps,
1. go to settings
2. under wireless & Networks settings hit more… button

[Solved] Sony Xperia C Signal Problem

3. on next page go to Mobile networks

[Solved] Sony Xperia C Signal Problem

4. on next page hit select Sim Card (chose sim1)

[Solved] Sony Xperia C Signal Problem

5. Then hit  Network Mode & Select GSM Only ( it should be on WCDMA preferred )

[Solved] Sony Xperia C Signal Problem

[Solved] Sony Xperia C Signal Problem

when you have GSM sim , you are no way using WCDMA , but chosing this option forces phone to use WCDMA network, which is not available by your service provider,
GSM & WCDMA operate in different way,

wait 2 minutes and your phone start showing full signals on sim1