Ping.
If your ping to the server is 100 or more, don't join.
You can sort the server list by ping (lowest to highest). Join servers with the lowest ping and you won't have lag.
75 ping or less is optimal.
My download speed is 434kb/s
and my upload speed is 97.8kb/s
is that kB/s or as you wrote kb/s, if it is 97.8kb/s then that it to low
Download Speed: 3474 kbps (434kB/s)
Upload Speed : 782 kbps (97.8kB/s)
That are the results from broadbandspeed.co.uk