Default settings for NICs is good for most cases however there are times when you need to do some performance tuning.
When you start to observe increasing drops of RX packets it means that your system cannot process incoming packets fast enough. You can verify on your monitoring system to correlate this issue with increased network traffic at the same time.
# ifconfig
eth0      Link encap:Ethernet  HWaddr 00:22:19:50:ea:76
inet addr:192.168.x.x  Bcast:192.168.x.x  Mask:255.255.xxx.xxx
UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
RX packets:3208932 errors:0 dropped:19188 overruns:0 frame:0
TX packets:1543138 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000First verify current NIC settings:
# ethtool -g eth0
Ring parameters for eth0:
Pre-set maximums:
RX:             1020
RX Mini:        0
RX Jumbo:       4080
TX:             255
Current hardware settings:
RX:             255
RX Mini:        0
RX Jumbo:       0
TX:             255

Increasing ring buffer for rx should fix this issue:
# ethtool -G eth0 rx 512

To have this settings persistent make sure you add this command to /etc/rc.local script.