Hey there,
Social anxiety is what keeps me trapped inside from time to time (and has een recently rearing it's ugly head again) so here is my 2 cents worth.
* If at all possible find a doctor you like - ask for recommendations, shop around etc so you end up seeing a regualr person who doesn't set your teeth on edge or make you dread seeing them. This can be a lengthy process but in my experience has been worth perservering with, as I am now addressing health issues I have ignored for years at my 'just gimme a script' doctor, or taking whoever is avaiable at the bulk bill place.
* I know my boundaries, and I write them down. There are somethings I do not do, or will not discuss wtih certain professionals. I make sure I know my boundaries and they know them too, up front.
* I know what I want from the visit/session, and I write it down. If I am coming to renew a regularprescription, that is different form coming in to ask about trying a medication for the first time, and that is different from asking for a referral or advice on quitting smoking. Know what you want from your visit. I prepare notecards - If there is something I want to ask about I write a note card, if I am worried they will criticise me (eg for smoking, me weight etc) I write a notecard of my position - I don't try to plan for every possible conversational scenario, but I put down my bottom lines so in the moment I won't get distracted/scared/intimidated/diverted etc.
* Online appointment bookings - how I love these! I can make my appointment on a whim when I am feeling strong, or motivated or whatever.... and I don't have to talk to anyone. But to cancel I DO have to call, so that's good incentive to keep it booked. I also tend to book appointments or make my follow up calls from work, because I am already in a very task oriented headspace and I get much lower phone avoidance at work.
* I nab the first appointment of the day so I can in-and-out as fast as possible and don't get stuck in a waiting room full of strangers for ages. I do a lot better if I set things up for early morning and just get out of bed and GO, with little or no time to talk myself out of it. I make sure I have my clothes, wallet, medicarecard, metcard, keys etc all set up the night before so in the morning there is nothing to look for or organise that I can work myself up over.
* For me if I am REALLY struggling to get out the door then I am much more likely to make it if a trusted friend or similar comes picks me up in their car and phsyically hauls my butt to where I need to be and gets me home again afterwards. (Taking a cab is also helpful, and again I like to prebook online).
* The appointment will most likely be ALL that happens on that day (sometimes even filling the script is too much for that day), and may well take a couple of days to bounce back from, so I try to factor that in and be aware of its impact on my normal daily life so I don't find myself getting down because I have been less productive/social/whatever than I expected to be.
* Have someone you can call, just in case. Soetimes drs will dump something new and scary on us at a routine visit, and the most carefully crafted plan of execution can't factor in all the possibilities. It can be helpful if you have a friend/family memeber/carer/hotline even to call afterwards just in case they stun you with something and your already stretched resources can't cope in the moment.
* Some kind of nice self soothing treat afterwards as a reward doesn't go astray - you did a hard thing and that's impressive. I usually feel drained and a love to have a nap to restore myself. I find daytime naps very comforting.
Hope this helps, at least a little.