Alot times then your playing multiplayer you begin to lag. This could be from a number of things, everything from someone playing an xbox, netflix, surfing the net, ect. Anything that uses an internet connection can affect you connection to a Minecraft Server. The best you can do is find what kind of ping you have to the server.

Ping is a Computer Network administration utility used to test the reach-ability of a host on an Internet Protocol (IP) network and to measure the round time for messages sent from then originating host to a destination computer.

Personally when I'm searching for a TF2 or COD server I look for the lowest ping however with minecraft I would recommend not using a server over 300ms. Everyone has a different opinion however I since minecraft is not completely instant updating (like most first person shooters) you can use a wider band of speed.

To test your connection to your favorite server use the directions below.

Windows 98/XP
To start this simple process
Click on Start
Click on Run
Type cmd and hit enter
Inn the command prompt type ping 'servername'

Windows Vista/7
Click on Start
In the search bar type cmd
Double-click on cmd
In the command prompt type ping 'servername'

Mac OS
Click on Findern in the dock.
Click on Macintoshn HD in the window.
Click on Applications.
Click non Utilies.
Double-click on Terminal.
Type ping 'servername'

Linux (any Flavor)
from the console
Type ping 'servername'

-example:
Ping josh.mcjoshmod.com

Pinging josh.mcjoshmod.com [66,225.231.234] nwith 32 bytes of data:
Reply from 66,225.231.234: bytes=32 time=12ms TTL=48
Reply from 66,225.231.234: bytes=32 time=10ms TTL=48
Reply from 66,225.231.234: bytes=32 time=15ms TTL=48
Reply from 66,225.231.234: bytes=32 time=22ms TTL=48

Ping statistics for 66.225.231.234:
Packets: Sent = 4, Received = 4, Lost = 0 <0% loss>,
Approximate round trip times in milli-seconds:
Minimum = 10ms, Maximum = 22ms, Average = 15ms

For more information you can use tracert in windows / traceroute in mac from the console / traceroute from the console in linux to determine where you could be lagging from or where the server might be located. Preferably you would want to pick a server with a low ping rate that is close to your location.

Full description.

In multiplayer online video games, pingn refers to the network latency between a player's computer (client), and either the game server or another client (i.e. peer). This could nbe reported quantitatively as an average time in milliseconds,n or qualitatively as low ping or high ping. The latter nusage is common among players of first-person shooter and real-time strategy games. Having a low ping is always ndesirable because lower latency provides smoother gameplayn by allowing faster updates of game data.

Ping is often conflated with lag. One may n"lag out" due to unacceptably high ping. Servers will often disconnect an client if the ping is too high and it poses a detriment to others' ngameplay. Similarly, client software will often mandate disconnection ifn the ping is too high. A high ping is not the result of lag; rather, a nhigh ping causes lag.