One of the most common questions in the gym is “should I do my weights or cardio first?”. There is no clear answer to this question for someone who is training for general health and fitness. The research is mixed and very limited in its scope. My recommendation is that if you want to train for strength, it is best to do a strength session only. If you want to improve your cardiovascular fitness it is best to do a cardiovascular session only. If you need to combine both to either make it more time-efficient or just because its more fun and you enjoy it then I recommend training your highest priority first. If you want more strength, do weights first. If you want more aerobic fitness, do your cardio first. There is really no right or wrong answer here. The most important thing is that you are actually training and every exercise that you do is giving you tremendous benefit no matter when you do it. Worrying less about what you are doing and more about just getting in and doing it will be a better approach to improve your health and fitness.
The same applies to stretching. Stretching before or after a session provides little to no difference in the benefit. The most critical element to improve flexibility is time spent stretching (chronic stretching). Most people will also improve their range of motion (ROM) by improving their strength and working their joints through angles and degrees of circumference that they haven’t done in a little while. Deep squats and overhead presses are common examples that highlight a limited range in joints we don’t need to use to their full capacity. Acute stretching before a session has been shown to decrease power which can affect your ability to lift heavy or run fast. Acute stretching after a session can exacerbate muscle damage that a hard training session has already caused. Confused? It may sound like stretching before or after a session is a bad idea but you’ll notice that most modern-day athletes use more dynamic stretches in their warm-ups and less static stretching for this reason. The decreased power and muscle damage caused by pre and post-session stretching is also reasonably negligible for the non-professional athletes of the world. A little less power and a little more damage won’t make a big difference to the health and fitness of casual exercisers. 
There are some less confusing tips for structuring your resistance exercises. Here is a summary:
•Do compound exercises first
•Do isolation exercises after compound exercises
•Pair exercises of the same body part to increase the focus and intensity
•Pair opposing and upper/lower body exercises for quicker recovery and greater kilojoule burn.
Comound exercises are exercises that work around more than one joint like bench press (elbow, shoulder, wrist) and squats (ankle, hip, knee). Isolation exercises work around only one joint like a bicep curl (elbow) or a leg extension (knee). The final consideration for your weights training should be how many reps and sets. There is a large amount of crossover training between the different protocols but here is a general guide to help you decide:
•Strength and hypertrophy (3-4 sets of 8-12 reps)
•Muscular Endurance (2-3 sets of 15-20 reps)
•Power (4-6 sets of 4-6 reps)
Good luck and happy training. If you would like further guidance make sure you email