Minecraft 1.8 Server Issue

Basically I just started using this website like 2 minutes ago and I've been searching for ages ever since 1.8 came out. I made a server and when I go o n it and when others go on it, it keeps saying 'cant keep up' and I dont know how to fix it! ive searched and searched for ages to fix this and thats when I found this website! So pretty much I need someone to help me get me server with no 'cant keep up' (no lag)

Thanks
-Darcy