well the first "trick" is stop trying to run your normal runs fast. If you are using the hard/easy training approach...you want your hard days to be "hardish" (actually you don't want to think about it as a hard effort but think of it more as a fast day or a volume day or some of both) and your easy days to be easy. many runners think they will improve faster by running faster on their easy days. Quite the opposite is true for multiple reasons.
1) running slow or easy on your recovery days allows you to recover better, so that you will be fresher on your hard workout days. Now get this, by going really easy - I mean 7:30-8:00 pace - i was getting up to 20-26 miles (about 3 hrs) of running in and was fine the next day to do my workouts. I am not suggesting that you do this...but it is something you can build up to. It took me some time to do this. the point is if the pace is easy - the effort is easy.
At one point in my post college running, i even experimented with not running on the easy days so that i would be really fresh for the hard days (i still trained, i just didn't run, i cross-trained). this allowed me to feel very good on hard days and the quality of my workout went way up (this happened gradually over time not over night). Not every day was fast. It seemed i would have one great workout like 10 miles at 5:20 pace and then the next workout would be more like 5:40 pace...probably because that is a pretty high quality effort and it can take the body a little time to recovery. But it worked. I ran between 25-40 miles per week and got considerably better (my prs dropped from 25:30 8k to 23:45). I still had a good base period previous to this. but the point is when the body needs rest, it needs rest, and easy days or days off are those resting efforts (running them too fast will not help you get better)
2) by running your easy days slower than normal you are actually stressing your body in a new way (burning more fat) which is why these slow run suck so much (at first) but in the end the benefits are huge.
Finally I will tell you that the only person who can tell how much you can increase your mileage is you (because you are the one feeling overly tired or not). Will you feel tired? yes, that is part of the process...and you should take a day off every so often (maybe once a week) during this build up... worry less about how many miles you are getting and more about how much volume you getting when you do run. Also trying to increase miles during a racing season can be tricky because you will be tired...it is best to do this during the off season, but if you are going to do it in season, expect to be tired and maybe even slower in early season racing until your body adapts.
For increasing mileage.
you can begin running two-a-days (this is a new stress and will make you tired so if you have never done this before you may try by doing this 2-3 times per week at first).
or you can gradually increase your recovery day distance at an easier pace (try going about 30 seconds per mile slower and add 2 miles to your normal run) if all goes well, try going even slower (another 30 seconds slower). Let say you had been running 6:30 pace on your easy days, try going 7:00 pace - that should feel really easy. this allows you to want to go further as the effort is really low. if that transition helps - go 7:30 pace and even further still. at some point maybe 8:00 pace, you are probably going about as slow as you will be able to tolerate (so no need to overdo the slow stuff here). the point is easy pace can be 7:00-8:00 pace...and some days you will find you will be at the lower end of that range and other days you will be at the upper end of that range. guess what? that is exactly what you want because it means you are listening to your body. You should not feel the same each day, and by adjusting the pace to how you feel you will always be running the right pace (easy is easy to whatever you body says feels right). the same is true of total miles. the right amount and progression is whatever you body can tolerate without overdoing it. how do you know if you are overdoing it. you get irritable, obsessive with your mileage total and run down = your start running slower on fast days and race days.