if you use the search function for and E36 buying guide, you will get a buyers guide.
I'm not very clued up on the BMW 4cyl engines, but they are pretty robust but do require a bit of regaular servicing and TLC to remain reliable and efficient. I'll leave this for those in the know like Ronnie and co.
Interiors are pretty hard wearing, even 150,000miles + cars should have an interior thats like new! Shabby and loose interior trim fitting = neglect, early models did suffer more so with poor interior trim fixings, so just ensure all the plastics are in place and not just hanging off. Seats should be in good condition with minimal wear signs on the drivers seat.
Brakes should be strong and free from judders, vibrations and noise. Tyres should be in good condition with even signs of wear on the same axle, irregular wear signs indicate suspension/streering problems.
Suspension parts such as bushes, mounts links etc have short service lives, so ensure the car tracks true and does not wander about the road and does not clonk and bang over rough surfaces and bumps. If it does budget circa £200 for suspension bush replacement. Rear springs can and do snap, so this is just something to be cautious of.
Also ignore spec levels like 'i', 'se' etc, BMWs are very poorly equipped so ensure the car you view has the creature comforts that you are looking for.
A good service history is essential, a lack of it can indicate clocking and nelect. Many BMWs fall into the hands of people who abuse these cars, don't pay the low enough service costs and those that tamper with mileages. The 316 and 318 models are popular, so BE fussy and there are enough good honest straight cars, with few owners and good service history records to choose from. Be willing to travel for the right car.
I have seen some nice sounding 316/318 models, with 2-3 owners and FSH, this is the sort of thing to go for and avoid car with many owners and a lack of service history as these will be the bad ones.