First I would re-iterate what abacus said about multiplying every expense by 10 to convert an expense to sales required to cover it. I had a boss ram this home 10 years ago and I have found it really useful as an employee managing budgets and as a business owner. I make sure my employees are aware of it as well. It really puts expenditure and losses into perspective and makes you really need stuff before spending.
The other question I ask my self is how much does the customer care about this. In your case how much does the customer care about what you spend on the fit out of your premises? Well quite a lot, they will expect an optometry practice to look clean, tidy and professional so it is worth spending up on quality equipment and fittings. However, how much does your customer care about your personal office that they will not go in to? Not much, so second hand desks and book-shelfs there then.
So for every expense multiply by 10 then ask how much your customer will care about it.
Specific recommendations: make sure on your merchant services you are charged a flat fee per transaction for debit cards not as a percentage. Shop around on your merchant services you may find some big savings because a fraction of a % on practically every sale will add up.
Rent is a big expense, don't be backwards in asking for a free period to get established or anything else you can think of that will help out.
Think really hard about your advertising you can chew through thousands to learn what works and what does not. I wrote about my early experiences and the money I wasted a while back: What are the biggest issues starting a business
Review your expenses every year. This year we had it a bit tough because we opened a new shop and invested lots of cash so profits were way down. This was actually really good because it made me take a long hard look at expenses. What we did:
Went into the bank a told them I thought I was paying too much for merchant services and asked how to get it reviewed. I left some details and ten minutes later I had a telephone call telling me they had reviewed my charges which would save me about $8k a year. It was really that easy.
After starting a thread and consulting with the good folks on FS I cut back on YP online to save $3k without loss of sales.
I took back my online advertising from an outsourced solution which is saving me about 15% on cost-per-click.
We started a record book on everything that goes wrong that causes inconvenience, lost time or cost.This was just a line or two about what happened, what was the cost to us, what was the impact on the customer and what we did about it. This gave mistakes an actual acknowledged value which makes people appreciate them more. It highlighted a few things that could be fixed and now it is actually quite rare to put stuff in the book.