The first race I ever ran was a full distance Marathon and I finished, so you can do it, too.
1) half distance is 13.1 miles and a nice distance to start with
2) buy very good running shoes
3) try to run outside, prob. 3-4 times a week with longer runs on the weekends
(this is what I do when I prepare for a marathon. You can check the internet. They offer whole training plans for free.)
4) I run 5 miles per session, one session per week is either fartlek,
hiit or hills, depends on what is required for the course (check the elevation chart of the course on the internet (if available) and plan your training accordingly>include running hills, if required)
5) eat lots of carbs. I prefer whole wheat bread, oat meal and whole wheat pasta
6) Do not eat whole wheat one day prior to race (to prevent possible bloating)
7) My longer runs are 6 miles, following weekend: 8 miles, following weekend: 10 miles, then 12 and then 14. Then:
8) 13.1 miles will not bother you too much on your race day.
9) If you run longer than 8/9 miles, bring food (carbs, that are easily digested: dried fruits work fine)
(I hit the wall after 9 miles, so I start eating after 8 miles)
10) Drink whenever you can (I drink water, gatorade only on race day and only mixed with water)
11) If you do weightlifting (I do, too) Run first and after that go to the gym (the same day), see what you can do (This is what my trainer told me to do and it works fine with me)
12) You may not be able to lift as heavy as usual, especially not after a challenging
hiit-session.
13) If you eat enough, you will not lose any weight. I am not an expert, though. I eat 60% carbs, 20 % protein, 20 % fat. I don not know, if this is right for you.
14) Include rest days in your schedule (I have two or three, my trainer sent me home sometimes, because I was doing too much without resting enough)
15) According to what plan you choose, one week before race YOU MUST NOT RUN. EAT CARBS. Some people however prefer to run one or two 20 minute sessions. I don't, but that is personal taste.
If you have questions, let me know.
The things described above work for me and other people I know. They, however, may not work for you. There is a lot of trial and error envolved.
Good luck