In answer to your questions:
Can you tell me pros and cons that come with signing a FRI lease?
There are no pros. An FRI lease means that you will become liable for paying for the cost of repairs and insurance of the building of which your shop forms part, usually with the landlord carrying out the work and recovering the costs from you via a service charge. If it is a standalone shop you may be required to do the works yourself (which is better as you have control over the costs). This is the standard type of commercial property lease and it in unlikely that you will get any other type of lease unless it is a short term lease of services offices, that kind of thing, or a very short letting.
What you need to know is that a commercial landlord expects the building to "wash its face" meaning that the series of tenants between them will pay for the upkeep of the building with the landlord never having to put his hand in his pocket.
There are many ways to minimise your exposure, however, which is why is it important not only to instruct a solicitor before you make an offer but also a surveyor to check the condition of the building.
What I need to look out for whilst doing an FRI?
Lots of things, too numerous to mention but you could start by reading this:
www.squidoo.com/commercialleases
When would really want a rental review?
Ideally never - they are usually upwards only - but if your lease is 10 years, the rent review commonly comes at year 5 and 10 (if your lease is not "contracted out") and at 3 yearly intervals if your lease is for 5 or 6 years. If your lease is shorter than that the you shouldn't have one altogether.
Break clauses??
Definitely. Again this depends on the lease term you are agreeing but work out how long you could survive financially if the business failed completely and put the break clause at that point. This can often be 1 year for a new business.
Hope this helps.