First of all connect the SainSmart 1.8" TFT display to a Raspberry Pi as described in the fbtft wiki. After this enable SPI by using the tool
$ sudo raspi-config
Or by adding the following line to the
/boot/config.txt config file.
After rebooting the Raspberry Pi load the required kernel module. As you might notice the communication speed has been decreased from 32MHz to 16MHz. This should make the connection more stable and reliable.
$ sudo modprobe fbtft_device name=sainsmart18 speed=16000000
The display should work now without any problems.