In planning for a cross-country flight, consider the topics covered by a briefer for a standard weather briefing. For weather information within 6 hours of your planned departure, all these should give some useful information. For my students, I recommend they sign up for an account on https://www.1800wxbrief.com/ prior to their first cross country flight.
1. Adverse conditions
My take is that adverse conditions come first to help determine if there’s anything that says, “don’t waste your time, you aren’t flying”. Almost any SIGMET over the area of my flight (assuming I can’t work around it) would be a pretty good indicator the flight is not advisable in a small plane. A quick check of SIGMETs here.
An AIRMET over the area of my flight at the planned time is a heads up to look more, but not as strong an indicator to cancel. For looking on a laptop, I usually use the graphical interactive version. From a smartphone, I find the static Airmet images easier to work with. Sierra airmets are best validated with current METARs, TAFs, and satellite images. Tango airmets are best validated with PIREPS, though lack of PIREPs is not the same as a PIREP telling you “negative turbulence”.
Briefers also seem to be giving TFRs in this part of the briefing now (seem reasonable, since some TFRs may keep you from flying).
This gives you an idea of what is driving the weather. This requires a better theoretical understanding of weather to help in augmenting other information you receive. A quick surface analysis chart will give you an idea. Think about where weather is moving, how winds will flow around high and low pressure, and whether slight changes in track or timing could cause you problems.
3. Current conditions
This is the place where you normally receive METAR information. Some people prefer entering a list of stations and some prefer a graphical representation. Also remember that some AWOS systems do not feed METAR information, but you can still call and get current information (see http://airnav.com/airport/F70 as an example).
4. Forecast conditions
This is where we receive area forecast and/or TAF information. I will look at TAFs for all available airports along or near my route of flight. However, remember that the nearest TAF may no be a good indicator for an airport that doesn’t have a TAF. Things like intervening terrain, proximity to the ocean and other effects should be considered. I prefer to get raw TAFs from a list of station identifiers.
5. Winds aloft
Again, some people like it graphically (this has the advantage of allowing you to look 3+ days out) and some like textual versions (remember to click on the region of interest). Remember to correlate this information with the synopsis and turbulence forecasts and reports and to calculate the impact on wind correction and ground speed.
This is an area where briefers seem to be pretty good at filtering through a pile of information (though they always seem keen to tell me that GPS satellite 24 is still out of service). Online, check https://pilotweb.nas.faa.gov/PilotWeb/