Go into the connection manager menu and change to EVDO only mode (HDR for Verizon) - that will tell the modem to only connect at the fastest speed (no roaming). If you don't have a EVDO capable tower nearby then no connection will be made. Turn this mode off when traveling.
Check the signal level on the connection manager, relocate to where strongest
If not using
Get MSL code from provider and change Home Agent via DATA menu (on some connection managers)
Use an external antenna to increase signal strength. Directional if fixed, Omni if mobile.
In addition to the above, if you have a USB modem put it on the end of a USB extension cable and move it around to find a good signal. These come in lengths of 10-15 ft and you can couple them to get your modem up higher or in a window.
Try the coffee can antenna, it works great.
A Note For Franklin CDU680 Owners:
If you are experiencing dropped connections there is a setting you need to be sure is not selected:
Go to Network Connections
Right click the Franklin Wireless icon - select Properties
Click the Networking tab
Click the Settings button
Make sure "Negotiate multi-link for single link connections" is not enabled
Also make sure you have not allowed Hibernation in the settings menu of the connection manager
A Note for Sierra 595U Owners:
This device has an internal battery which must be kept charged.
If the power falls below a certain level your speeds will be reduced.
Some USB ports do not put out adequate voltage to keep it fully charged, and if you are on laptop battery power the voltage can drop. This will discharge the 595U rapidly causing connection problems.
A powered USB adapter can remedy this problem if you are using a desktop. Using AC power or making sure your laptop is fully charged can help in a portable situation. Earlier shipments of this modem came with a Y-adapter that you could use in two USB ports to provide the necessary voltage. Apparently that is no longer supplied.
Sometimes you can get a better connection if you disconnect/reconnect to your provider. This will give you a new Default Gateway IP address. To see what your current address is go to a command prompt and type "netstat -nr ". This will give you a screen that shows your current Default Gateway on the bottom line:
You can obtain the same information by running a speed test at http://www.speedtest.net/
Simply disconnect/connect until this number changes to something new.