Wildcard mask is very different from subnet mask.
The values for subnet mask can be 128,192,224,240,248,252,254 and 255.
On the other hand, wild card mask values are: 127,63,31,15,7,3,1 and 0.
The tip out here is that simply subtract subnet mask value from 255.
In ACLS and OSPF network statements, we use wild card mask, 127 will be: 011111111 which means match the first bit and ignore the other 7.
I will try to post as many tips as i can in coming days.