Spinning a high cadence, like 90 pedal spins per minute, can help increase speed and endurance. You can get more speed by riding intervals, too: a few minutes very fast, recover a few minutes, go again. Try that about 5 times or so, once a week. Also, don't forget to take at least a day off a week, to let your body recover (and get stronger).
The 10% a week rule is smart (longest ride each week only 10% longer, to prevent injury). Once you go more than 70 minutes, nutrition/hydration and comfort begin to impact endurance. If you don't get enough water, calories, sodium, potassium, calcium, magnesium..., you can 'bonk' or get cramps. Give your body all that stuff, and it can do more without complaining. You'll ride further if you eat a little, and drink, while riding. You might also need to get a new saddle, or some clipless pedals, or make some minor adjustments to be more comfortable and/or efficient.
Core strength can help you go further and faster, too. Make sure you are not bouncing, rocking, swaying as you ride. Use your core muscles to keep you stable and put all your energy into forward motion. You don't need a kung fu grip on the handlebars (wasted energy).
You can get some good books at the library, or Barnes and Noble. Good luck.
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