I am building a plane so on which basis should I place  motor whether it is down trust towards left or how

Too many variables and insufficient data

Better go with an experienced and proven designer and follow his recommendations

Generally, right thrust is given to counter gyroscopic effect of the prop giving a tendency to turn left especially at take-off; downthrust to counter the tendency to climb excessively under power. But it is not always needed.

You could make it zero thrust, and then add washers according to the model's behaviour. But as a beginner, who even needs to ask this question, you would be better off sticking to a good designer's recommendation

For 1 meter length wingspan and body length is 30 inch which electronics would you suggest

Firstly determine the weight

Plane weight is 250 g without any electronics only depron foam

3 or 4 X 9 gm servos, Rx, 1500 mah 3S LiPo battery, 30 A esc, wiring, landing gear + approx. 50 gm for motor = ~ 300 gm

Total weight 550 gram. A thrust of 600 gm plus will ensure good performance, and power needed is about 130-175 Watts

Suitable motor/prop are many. eg 2826-1400 with a 7*4 prop

CAN I use 1800 mah 3 s 30c lipo

Sure you can. I don't know your wing area (only span, not chord) but if the wing loading is high (gm/sq. cm) the model will fly pretty fast, will not have very good low speed handling, and poorer glide entailing a higher landing speed 

If you have a 1300 mah you could reduce about 50 grams!

But again, a lot depends on the model design..... the only way now is to fly it  >