How can I make sure fuel is getting to the motor after changing the filter on my boat?

If you have a fuel injected engine, then after installing the new filter, turn the ignition key to the "on" position (not "start") for a few seconds. Listen for the faint whine of the electric fuel pump building pressure. Turn the key off when you hear the pump stop. Turn the key on again. If the fuel pump starts VERY briefly, that means you have filled the filter and the system has pressurized. If the fuel pump runs longer than a second, repeat the off-on cycle a few more times. If your engine is not fuel injected, then consult a local marine mechanic - priming fuel systems on carbureated boat engines is beyond the scope of online DIY advice.