If other lines connected to gnd it doesn't matter, I leave them open.

Important is only initialization sequence.

Write:
03 - in 8bit mode (EN=1,EN=0)
delay 6ms
03 - in 8bit mode
200 us delay
03 - in 8bit mode
200 us delay
02 - in 8bit mode
then you can start with 4bit mode write
2ch - write in 4-bit mode

Take care of the delays that are very important for timings.

I have used above initialization routine for at least 5 different types of LCD modules and runs OK. I had to extend some delays at first for some different types of modules.

Hope this helps.