If your under 16 dont weight train, its bad for you.
If your over 16 then do it in the morning. A basic workout i used in the past was this.
Incline Dumbbell Press, Flat dumbbell press, Dumbbell flys,3 different types of tricep extension, it varies for me, i like to keep it fresh, and lots and lots of dips. Then a core workout, and end with 2-5 mile run.
upright row, bent over row, lat pulldown, lat raises, rear deltoid machine, 3 of the many types of bicep workouts, then i do legs, Core 2-5 mile run.
I respectfully Disagree. Weight Training has no negative effect on younger populations.
Also, If you've never done serious strength Training* before, a program like Starting strength or Stronglifts would be AWESOME for you. check the Starting strength wiki, and stronglifts website. It's worth digging around for the right information (both sites are hard to navigate).
Ideally, you would do nothing but strength work to get the most out of the program, but there are a lot of people (Including serious competitors) who train strength and MMA on similar programs.
Try to put 8-12 hours between fight training and weight training, and if your exhausted don' weight train one day to let your body recover, your body wont make good gains if you never give it a chance to recover.
This is good advice.
If you're SUPER tired after training, do strength on the off days (your two days off and one Muay Thai day). If you're still pretty fresh, you could do it the same day, or the next morning. Strength gains occur during the recovery phase.
* Strenght Training is different to bodybuilding.